Ceramic filter for exhaust gas emission control

ABSTRACT

A ceramic filter assembly that resists cracking. The ceramic filter assembly is formed by integrating a plurality of columnar honeycomb filters made of a porous ceramic sintered material with a ceramic sealing material layer and formed to have a substantially elliptical cross sectional shape. The honeycomb filters includes square columnar honeycomb filters in which the ratio between the lengths of their long sides and short sides is between 1.1 and 3.0. The honeycomb filters are arranged so that the long sides and the short sides are respectively parallel to the major axis and the minor axis of the assembly.

TITLE OF THE INVENTION CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Application No.2002-72847, filed on Mar. 15, 2002, the contents of which are herebyincorporated herein reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to ceramic filters for exhaust gasemission control, and more particularly, to a ceramic filter assembly inwhich a plurality of filters made of a ceramic sintered material areintegrated, a canning body, and a columnar honeycomb filter that may beused when manufacturing the same.

DESCRIPTION OF THE RELATED ART

The number of automobiles is dramatically increasing, and in proportionthereto, the amount of exhaust gas exhausted from internal combustionengines of automobile is also rapidly increasing. Various substancescontained in the exhaust gas, especially from diesel engines causepollution, and thus presently, are seriously affecting the worldenvironment. Reports have been recently made on study results that fineparticles (diesel particulate) in the exhaust gas may sometimes causeallergic symptoms or reduce sperm counts. A measure for eliminating thefine particles in the exhaust gas is thus an urgent problem that must becoped with for the sake of mankind.

Accordingly, a variety of exhaust gas purifying devices have beenproposed in the prior art. A typical exhaust gas purifying device has aconfiguration in which a casing is arranged on an exhaust pipe coupledto an exhaust manifold of an engine, and a filter including fine holesis arranged therein. The filter may be made of, besides metal and metalalloy, ceramic. A known example of a filter made of ceramic includes ahoneycomb filter made of cordierite. Recently, a porous silicon carbidesintered material is often used as the material forming the filterbecause of the advantages of, for example, high thermal resistance, highmechanical strength, high collecting efficiency, chemical stability, andsmall pressure loss (e.g., Japanese Laid-Open Patent Publication No.2001-162119).

The honeycomb filter has multiple cells (through-holes) extending in anaxial direction thereof. When exhaust gas passes through the filter, thefine particles are trapped at the cell walls of the filter. As a result,the fine particles are removed from the exhaust gas.

However, since the honeycomb filter made of a porous silicon carbidesintered material has large thermal expansion, as the size of the filterincreases, cracks tend to occur in the filter during use at hightemperature. Thus, a technique for manufacturing one large ceramicfilter assembly by integrating a plurality of small filter pieces hasbeen recently proposed as a means for avoiding damage caused by cracks.

A general method for manufacturing the above mentioned assembly will nowbe briefly introduced.

First, a square columnar shaped honeycomb molded product is formed bycontinuously extruding a ceramic material through a metal mold die of anextruder. After cutting the honeycomb molded product into equal lengths,each cut piece is sintered to produce a filter. After the sintering, theouter surfaces of the filters are adhered to each other by a ceramicsealing material layer to bundle and integrate the filters.Consequently, the desired ceramic filter assembly is completed. A matthermal insulation material including ceramic fibers and the like iswrapped around the outer surface of the ceramic filter assembly. Theassembly in such state is accommodated within a casing arranged on theexhaust pipe.

[Patent Publication 1]

Japanese Patent Publication No. 2001-162119

In case of a filter having an integrated structure and a cross sectionthat is oblong, such as, a substantially elliptical shape, it is foundthat cracks are more likely to occur in filters located at peripheralportions rather than at central portions of the assembly. When observingthe filter assembly after repeating reproduction a number of times anddividing the filter assembly, a slight amount of burnt residue of sootwas found for the first time in filters located at the peripheralportions. It can thus be presumed that a temperature difference existsbetween individual honeycomb filters. This causes a difference in thereproduction level during a single reproducing process. Further, thesoot residue causes a difference in the subsequent collecting amount,and the temperature stress due to the difference in the amount of sootduring reproduction causes cracks in the honeycomb filter.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a ceramic filterassembly having superior strength. It is a further aspect of the presentinvention to provide a columnar honeycomb filter suitable formanufacturing such a ceramic filter assembly.

The inventor of the present invention has recognized that in an exhaustgas purifying device connected to an engine through a pipe having aninner diameter smaller than the filter, a temperature difference isproduced between a central portion and a peripheral portion of thefilter assembly when the pipe is conically enlarged just before thefilter.

Further, the inventor of the present invention has recognized that in afilter assembly having an oblong shape such as substantially ellipticalshape, a large temperature difference is produced between the peripheralportion in the major axis direction and the peripheral portion in theminor axis due to difference in the distance from the central portion.The inventor has confirmed that this temperature difference preventsuniform reproduction, produces residual soot, and cause cracking whenthe filter exceeds its strength limit.

Based on the above knowledge, the inventor has conducted tests andresearch to manufacture an oblong filter assembly enabling uniformtemperature rise. As a result, it has become understood that if theceramic filter assembly is manufactured so as to satisfy certainconditions, thermal stress would be absorbed and a ceramic filterassembly having superior strength would be manufactured.

Accordingly, a conclusion has been reached that in order to uniformlytransfer heat from the central portion to the peripheral portion, acondition in which the thermal conductivity in the major axis directionis higher than the thermal conductivity in the minor axis direction,particularly, a condition in which the heat insulating effect isincreased at the peripheral portion of the assembly in the major axisdirection compared to the peripheral portion in the minor axis directionshould be satisfied.

The present inventions provides a ceramic filter assembly integrated byadhering together a plurality of columnar honeycomb filters made of aporous ceramic sintered material with a ceramic sealing material layerand having a substantially elliptical cross sectional shape when cutparallel to end faces of the plurality of honeycomb filters.

In a first aspect, the plurality of honeycomb filters include ahoneycomb filter having a rectangular cross sectional shape when cutparallel to the end faces and provided with a long side having length B1and a short side having length B2 in which the ratio B1/B2 is between1.1 and 3.0. The honeycomb filter is arranged so that the long side andthe short side of the honeycomb filter are respectively parallel to themajor axis and minor axis of the assembly.

In a second aspect of the present invention, each honeycomb filterincludes a plurality of rectangular cells extending along an axis of thefilter with each cell provided with a long side having length C1 and ashort side having length C2 in which the ratio C1/C2 is between 1.1 and3.0. The plurality of honeycomb filters are arranged so that the longsides of the cells are parallel to the major axis of the assembly andthe short sides of the cells are parallel to the minor axis of theassembly.

In a third aspect, each honeycomb filter includes a plurality ofrectangular cells extending along an axis of the filter and defined byrelatively thick cell walls and relatively thin walls that areorthogonal to each other. The plurality of honeycomb filters arearranged so that the relatively thick cell walls are parallel to themajor axis of the assembly and the relatively thin cell walls areparallel to the minor axis of the assembly.

In a fourth aspect, the ceramic sealing material layer includes a firstsealing material layer extending parallel to the major axis of theassembly and a second sealing material layer extending orthogonal to themajor axis of the assembly. The first sealing material layer is thickerthan the second sealing material layer.

In a fifth aspect, the ceramic sealing material layer includes a firstsealing material layer parallel to the major axis of the assembly and asecond sealing material layer orthogonal to the major axis of theassembly. The first sealing material layer has a thermal conductivitylower than the thermal conductivity of the second sealing materiallayer.

In a sixth aspect, the ceramic filter assembly further includes an outersealing material layer made of ceramic and formed on the periphery ofthe assembly. The outer sealing material layer includes a first portionlocated along an extension of the major axis of the assembly that isthicker than a second portion located along an extension of the minoraxis of the assembly.

In a seventh aspect, a ceramic filter assembly integrated by adheringtogether a plurality of columnar honeycomb filters made of a porousceramic sintered material with an inner sealing material layer made ofceramic and has a generally elliptical cross sectional shape when cutparallel to end faces of the plurality of honeycomb filters is provided.A tubular casing accommodates the ceramic filter assembly. A thermalinsulation material is arranged between the casing and the ceramicfilter assembly. The thermal insulation material includes a firstportion located along an extension of the major axis of the assembly anda second portion located along an extension of the minor axis of theassembly. The first portion is thicker than the second portion.

In an eighth aspect, a columnar honeycomb filter made of a porousceramic sintered material is provided. The honeycomb filter has arectangular cross sectional shape when cut parallel to an end facethereof and is provided with a long side having length B1 and a shortside having length B2 in which the ratio the B1/B2 is 3.0 or less.

In a ninth aspect, the columnar honeycomb includes a plurality of cells,extending along the axial direction thereof, and an end face. Each cellhas a rectangular cross sectional shape when cut parallel to the endface. Each cell is provided with a long side having length C1 and ashort side having length C2 in which the ratio C1/C2 is 3.0 or less.

In a tenth aspect, a columnar honeycomb filter made of a porous ceramicsintered material includes a plurality of rectangular cells extendingalong the axial direction of the honeycomb filter. Each rectangular cellis defined by a relatively thick cell wall and a relatively thin cellwall that are orthogonal to each other.

In an eleventh aspect, in a ceramic filter assembly having asubstantially elliptical cross sectional shape, when a hypotheticalfirst straight line intersects the generally elliptical contour at twopoints in which the distance therebetween is maximum and a hypotheticalsecond straight line orthogonal to the first straight line intersectsthe generally elliptical contour at two points in which the distancetherebetween is maximum, the number of sealing material layers that thefirst straight line of the assembly traverses is less than or equal tothe number of sealing material layers that the second straight linetraverses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an exhaust gas purifying deviceincluding a ceramic filter assembly according to one embodiment of thepresent invention;

FIG. 2 is a perspective view showing the ceramic filter assembly of FIG.1;

FIG. 3( a) is a perspective view showing a honeycomb filter having arectangular cross section;

FIG. 3( b) is a perspective view showing a honeycomb filter having arectangular cell;

FIG. 3( c) is a perspective view showing a honeycomb filter having aplurality of cells partitioned by cell walls that are orthogonal to eachother and have different thicknesses;

FIG. 4 is a cross sectional view showing the exhaust gas purifyingdevice of FIG. 1;

FIGS. 5( a) to 5(e) are views showing cross sectional shapes of theceramic filter assembly;

FIG. 6( a) is a side view of the filter assembly formed from a honeycombfilter having a rectangular cross section;

FIGS. 6( b) and 6(c) are side views of the filter assembly formed from ahoneycomb filter having a square cross section;

FIGS. 7( a), 7(b), and 7(c) are side views of the filter assembly formedfrom a honeycomb filter having cells of different shapes;

FIGS. 8( a), 8(b), and 8(c) are side views of a filter assembly formedfrom a honeycomb filter having walls of different thicknesses;

FIGS. 9( a), 9(b), and 9(c) are side views of the filter assemblyintegrated with a sealing material layer of different thickness;

FIG. 10( a) is a side-view of the filter assembly integrated by asealing material layer of different thermal conductivity;

FIG. 10( b) is a side view of the filter assembly including an exteriorsealing material layer of uneven thickness; and

FIG. 10( c) is a side view of the filter assembly including a thermalinsulation material of uneven thickness.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An exhaust gas purifying device 1 according to one embodiment of thepresent invention will now be described.

As shown in FIG. 1, the exhaust gas purifying device 1 is a device forpurifying exhaust gas discharged from a diesel engine 2 serving as aninternal combustion engine. The diesel engine 2 includes a plurality ofcylinders (not shown). Each cylinder is connected to a branch pipe 4 ofan exhaust manifold 3 that is made of a metal material. Each branch pipe4 is connected to a single manifold body 5. Accordingly, the exhaust gasdischarged from each cylinder pipe is concentrated at one location.

A first exhaust pipe 6 and a second exhaust pipe 7 made of a metalmaterial are arranged downstream of the exhaust manifold 3. An upstreamend of the first exhaust pipe 6 is coupled to the manifold body 5. Atubular casing 8, also made of a metal material, is arranged between thefirst exhaust pipe 6 and the second exhaust pipe 7. An upstream end ofthe casing 8 is coupled to a downstream end of the first exhaust pipe 6,and a downstream end of the casing 8 is coupled to an upstream end ofthe second exhaust pipe 7. The exhaust gas flows through the firstexhaust pipe 6, the casing 8, and the second exhaust pipe 7.

As shown in FIG. 1, a central portion of the casing 8 has a greaterdiameter than the exhaust pipes 6, 7. That is, the interior of thecasing 8 is larger than that of the exhaust pipes 6, 7. A ceramic filterassembly 9 is accommodated in the casing 8. The exhaust gas purifyingdevice 1 accommodating the ceramic filter assembly 9 in the casing 8 isreferred to as a canning body.

A thermal insulation material 10 is arranged between the outer surfaceof the assembly 9 and the inner surface of the casing 8. The thermalinsulation material 10 is a mat-shaped body formed from ceramic fibers,and has a thickness of 2 mm to 60 mm. The thermal insulation material 10preferably has an elastic structure and has a function for releasingthermal stress. The thermal insulation material 10 minimizes energy lossduring reproduction by preventing heat from escaping from the outermostportion of the assembly 9. Further, due to the elastic structure, theceramic filter assembly 9 is prevented from being displaced by thepressure of the exhaust gas and vibrations when the vehicle istraveling.

The ceramic filter assembly 9 of the present embodiment is for removingdiesel particulates as mentioned above, and is thus normally referred toas a diesel particulate filter (DPF). As shown in FIG. 2 and FIG. 4, theassembly 9 of the present embodiment is formed by bundling andintegrating a plurality of honeycomb filters F1. Among the plurality ofhoneycomb filters F1, the honeycomb filters F1 located at the centralportion of the assembly 9 each has a square columnar shape, as shown inFIGS. 3( a) to 3(C). Honeycomb filters F1 having a shape other than asquare columnar shape are arranged around the square columnar shapedhoneycomb filters F1. As a result, when seen as a whole, the ceramicfilter assembly 9 has a substantially elliptic cylinder shape with asubstantially elliptical cross sectional shape.

The cross section of the assembly 9 of the present invention issubstantially elliptical. “Substantially elliptical” is not limited onlyto an ellipse configured only by curves, as shown in FIG. 5( a). Anoblong elliptical shape partially having, for example, straight lines asshown in FIG. 5( b), more specifically, a pair of straight parallellines to each other is also included. The straight portion may only beat one section, or may be at more than three sections. “Oblong” includesshapes as shown in FIG. 5( a), FIG. 5( b), FIG. 5( c), FIG. 5( d), andFIG. 5( e). The lengths of the major axis and minor axis of the assembly9 are defined as A1 and A2 (A1>A2), respectively. If the substantiallyelliptical shape is an ellipse, a long axis passing a focal point is themajor axis, and a short axis orthogonal thereto is the minor axis. Thedimensions A1 and A2 are preferably 500 mm or less. If the dimensions A1and A2 are greater than 500 mm, it becomes difficult to manufacture theassembly with sufficient strength.

The length L (mm) of each honeycomb filter F1 is defined as thedimension of the direction in which the exhaust gas or fluid subjectedto treatment flows (direction orthogonal to the end face of the filter).When each honeycomb filter F1 is cut perpendicular to the flow directionof the exhaust gas (that is, cut parallel to the end face of thefilter), the cross section is rectangular. The lengths (outsidedimension) of the long side and the short side of the cross section ofthe honeycomb filter F1 are defined as B1 and B2 (B1≧B2), respectively.Each of the dimensions B1 and B2 are preferably 110 mm or less. This isbecause the strength of the filter F1 decreases significantly when thedimensions B1 and B2 are greater than 110 mm.

It is preferred that the ratio of B1/B2 be 3 or less. This is because ifthe ratio of B1/B2 is greater than 3, thermal stress is more likely toact on the filter F1 due to thermal shock, and cracks are more likely tooccur.

The honeycomb filter F1 is made of a porous silicon carbide sinteredmaterial, which is one type of porous ceramic sintered material. Thesilicon carbide sintered material is used because of its excellentthermal resistance and heat conductivity when compared to otherceramics. Instead of silicon carbide, the sintered material may be madeof, for example, silicon nitride, sialon, alumina, cordierite, mullite,and the like.

Silicic ceramics in which metal silicon is mixed to the above mentionedceramic, and ceramics bonded with silicon and silicate compound may alsobe used. This is because the metal silicon prevents cracks caused bythermal shock and the like.

It is preferred that 5 to 50 parts by weight of metal silicon isincluded per 100 parts by weight of silicon carbide. If the amount ofmetal silicon is too small, the adhesive strength of the filter F1decreases, and if the amount is too large, the filter F1 becomes denseand the properties necessary as the filter cannot be obtained.

As shown in, for example, FIG. 3( a) to FIG. 3( c), each honeycombfilter F1 has a so-called honeycomb structure. The honeycomb structureis adopted because the pressure loss is small even if the collectedamount of fine particles increases. Each honeycomb filter F1 includes aplurality of cells 12 (through-holes) having a rectangular crosssection, regularly formed in the axial direction thereof. The lengths ofthe sides (inner diameter) of the rectangular cross section of each cell12 are defined as C1 and C2 (C1≧C2). The cells 12 are partitioned fromeach other by thin cell walls 13 a and 13 b. The thickness of the cellwalls 13 a, 13 b are defined as D1 and D2 (D1≧D2), respectively.

The ratio C1/C2 is preferably 3 or less. This is because if the ratioC1/C2 is greater than 3, thermal stress is more likely to act on thefilter F1 due to thermal shock, and cracks are more likely to occur.

The ratio D1/D2 is preferably 3 or less. This is because if the ratioD1/D2 is greater than 3, thermal stress is more likely to act on thefilter F1 due to thermal shock, and cracks are more likely to occur.

An oxidation catalyst made of platinum group elements (e.g., Pt) andother metal elements and oxides thereof are carried by the cell walls 13a and 13 b. Each cell 12 is sealed with a plug 14 (made of a poroussilicon carbide sintered material in this embodiment) at either one ofthe end faces 9α and 9β of the filter F1. A checker-board like patternis formed on the end faces 9α and 9β by the sealed cells 12. The densityof the cell 12 is preferably approximately 200 cells/square inch. Abouthalf of the cells 12 are open at the upstream side end face 9α and theremaining cells 12 are open at the downstream side end face 9β. Thelengths C1, C2 of the sides of the cell 12 are preferably set between0.5 mm and 5.0 mm. If the dimensions C1, C2 are greater than 5.0 mm, thefiltering surface area of the cell walls 13 a and 13 b becomes small.This lowers the performance of the filter F1. On the other hand, if thedimensions C1 and C2 are smaller than 0.5 mm, the filter F1 becomes verydifficult to manufacture. The thicknesses D1, D2 of the cell walls 13 a,13 b are preferably set between 0.1 to 0.5 mm. This is because if thedimensions D1 and D2 are greater than 0.5 mm, the fluid resistance(pressure loss) produced by the filter F1 becomes high and is thus notsatisfactory. If, on the other hand, the dimensions D1 and D2 aresmaller than 0.1 mm, the strength of the filter F1 becomes insufficient.

The average pore diameter of the honeycomb filter F1 is preferablybetween 1 μm and 50 μm, and more preferably, between 5 μm and 20 μm. Ifthe average pore diameter is less than 1 μm, the honeycomb filter F1would often become clogged by the deposition of fine particles. If, onthe other hand, the average pore diameter exceeds 50 μm, small fineparticles cannot be collected. This would reduce the collectingefficiency.

The porosity of the honeycomb filter F1 is preferably between 30% and80%, and more preferably, between 40% and 60%. If the porosity is lessthan 30%, the honeycomb filter F1 becomes too dense and may not allowthe passage of exhaust gas. If the porosity exceeds 80%, the amount ofgaps formed in the honeycomb filter F1 becomes excessive. This wouldweaken the strength and decrease the collecting efficiency of the fineparticles.

When a porous silicon carbide sintered material is selected, the thermalconductivity of the honeycomb filter F1 is preferably between 5 W/m·Kand 80 W/m·K, and more preferably, between 30 W/m·K and 70 W/m·K.

As shown in FIG. 2, FIG. 4, and FIG. 10( a), the outer surfaces of thehoneycomb filters F1 are adhered to each other by means of ceramicsealing material layers 15 a and 15 b. The ceramic sealing materiallayers 15 a and 15 b are defined to be of the same type for those thatare parallel to each other. Hereinafter, the ceramic sealing materiallayers parallel to the long side of the assembly 9 are denoted by 15 a,the thickness of which is E1, the thermal conductivity of which is G1.The ceramic sealing material layers parallel to the short side of theassembly 9 is denoted by 15 b, the thickness of which is E2 (E1≧E2), andthe thermal conductivity of which is G2. The ratio of E1/E2 ispreferably equal to or less than 5. If the ratio El/E2 is greater than5, the heat conduction reverses between the short side direction and thelong side direction, and thus a uniform temperature rise of the assembly9 becomes difficult. The ratio E1/E2 is preferably 1.05 or greater. Ifthe ratio E1/E2 is less than 1.05, thermal conduction in the directionof the long side becomes difficult. Thus, uniform temperature rise ofthe assembly 9 becomes difficult. This produces soot and cracks becomelikely to occur.

If the thicknesses of the sealing material layers 15 a and 15 b are thesame, the thermal conductivity G1 and G2 of both sealing material layers15 a and 15 b may be adjusted by differing the compositions (compound)of the sealing material layers 15 a and 15 b from each other. In thiscase, the ratio G1/G2 is preferably 0.20 or greater. If the ratio G1/G2is smaller than 0.20, the thermal conduction reverses between the shortside direction and the long side direction, and thus a uniformtemperature rise of the assembly 9 becomes difficult. The ratio G1/G2 ispreferably 0.7 or less. If the ratio G1/G2 is greater than 0.7, thethermal conduction in the direction of the long side becomes difficult.This produces soot and cracks become likely to occur.

The ceramic sealing material layers 15 a, 15 b of the present inventionwill now be described in detail.

The thicknesses E1 and E2 of the sealing material layers 15 a and 15 bare preferably between 0.3 mm and 3 mm, and more preferably between 0.5mm and 2 mm. If the thicknesses E1 and E2 exceed 3 mm, the thermalresistance of the sealing material layers 15 a and 15 b become largeeven if the thermal conductivity is high, thus inhibiting the thermalconduction between the honeycomb filters F1. The percentage of thehoneycomb filters F1 occupying the assembly 9 also relatively decreases,thus leading to lower filtering performance. If, on the other hand, thethicknesses E1 and E2 of the sealing material layers 15 a and 15 b areless than 0.3 mm, the thermal resistance will not be large but the forceadhering the honeycomb filters F1 to each other becomes insufficient,and thus the assembly 9 is likely to break.

The sealing material layers 15 a and 15 b include at least inorganicfibers, an inorganic binder, an organic binder, and inorganic particles.Further, the sealing material layers 15 a and 15 b preferably made of anelastic material formed by bonding the inorganic fibers and theinorganic particles with the inorganic binder and the organic binder.

The inorganic fiber contained in the sealing material layers 15 a and 15b include at least one or more types of ceramic fiber selected fromsilica-alumina fiber, mullite fiber, alumina fiber, and silica fiber.Among these fibers, silica-alumina ceramic fiber is particularlypreferable. This is because silica-alumina ceramic fiber has excellentelasticity and exhibits thermal stress absorbing performance.

The content of the silica-alumina ceramic fiber in the sealing materiallayers 15 a and 15 b is 10% by weight to 70% by weight, preferably 10%by weight to 40% by weight, and more preferably, 20% by weight to 30% byweight in solid content. If the content of the silica-alumina ceramicfiber is less than 10% by weight in the solid content, the effect as anelastic body decreases. If the content of the silica-alumina ceramicfiber exceeds 70% by weight, not only does the thermal conductivitydecrease, but elasticity also decreases.

Shot content in the silica-alumina ceramic fiber is 1% by weight to 10%by weight, preferably 1% by weight to 5% by weight, and more preferably,1% by weight to 3%. If the shot content is less than 1% by weight,manufacturing becomes difficult. If, on the other hand, the shot contentexceeds 50% by weight, the outer surface of the honeycomb filter F1tends to be damaged.

The fiber length of the silica-alumina ceramic fiber is 1 μm to 100 mm,preferably, 1 μm to 50 mm, and more preferably, 1 μm to 20 mm. If thefiber length is shorter than 1 μm, an elastic structure cannot beformed. If the fiber length exceeds 100 mm, fuzzballs of fibers areformed. This lowers dispersion of the inorganic fine particles. Further,it becomes difficult to make the sealing material layers 15 a and 15 bless than or equal to 3 mm, and the thermal conductivity between thehoneycomb filters F1 cannot be improved.

The inorganic binder contained in the sealing material layers 15 a and15 b is preferably at least one or more types of colloidal sol selectedfrom silica sol and alumina sol. Among these sols, silica sol isparticularly preferable. This is because silica sol is easy to obtain,easily becomes SiO₂ by performing sintering, and is thus suitable as anadhesive agent under high temperatures. Furthermore, silica sol hassuperior insulation.

The content of the silica sol in the sealing material layers 15 a and 15b is 1% by weight to 30% by weight, preferably, 1% by weight to 15% byweight, and more preferably, 5% by weight to 9% by weight in solidcontent. If the content of the silica sol is less than 1% by weight, theadhesion strength decreases. If the content of the silica sol exceeds30% by weight, this may reduce thermal conductivity.

The organic binder contained in the sealing material layers 15 a and 15b is preferably a hydrophilic organic macromolecule, and morepreferably, at least one or more types of polysaccharide selected frompolyvinyl alcohol, methyl cellulose, ethyl cellulose, and carboxymethylcellulose. Among these, carboxymethyl cellulose is particularlypreferable. This is because carboxymethyl cellulose produces suitablefluidity for the sealing material layers 15 a and 15 b and thus exhibitsexcellent adhesiveness under normal temperatures.

The content of the carboxymethyl cellulose in the sealing materiallayers 15 a and 15 b is 0.1% by weight to 5.0% by weight, preferably,0.2% by weight to 1.0% by weight, and more preferably, 0.4% by weight to0.6% by weight in solid content. If the content of the carboxymethylcellulose is less than 0.1% by weight, migration can not be sufficientlysuppressed. “Migration” is a phenomenon in which the binder in thesealing material layers 15 a and 15 b migrates as the solvent is driedand removed when the sealing material layers 15 a and 15 b filledbetween the subjected sealing body cure. If the content of thecarboxymethyl cellulose exceeds 5% by weight, the organic binder isburnt by the high temperature and the strength of the sealing materiallayers 15 a and 15 b is lowered.

The inorganic particles contained in the sealing material layers 15 aand 15 b is preferably an elastic material using a whisker or at leastone or more types of inorganic powder selected from silicon carbide,silicon nitride, and boron nitride. Such carbides and nitrides have verylarge thermal conductivities, and are arranged on the ceramic fibersurface or on the surface and the inside of the colloidal sol andcontribute to the enhancement of thermal conduction.

Among the inorganic particles of the above carbides and nitrides,silicon carbide powder is particularly preferable. This is becausesilicon carbide has an extremely high thermal conductivity, and inaddition, has affinity for ceramic fiber. Moreover, this is because thehoneycomb filter F1 serving as the subjected sealing body is of the sametype, in other words, is made of porous silicon carbide in the presentembodiment.

The content of silicon carbide powder is 3% by weight to 80% by weight,preferably, 10% by weight to 60% by weight, and more preferably, 20% byweight to 40% by weight in solid content. If the content of the siliconcarbide powder is less than 3% by weight, the thermal conductivity ofthe sealing material layers 15 a and 15 b decreases and causes thesealing material layers 15 a and 15 b to remain as a large thermalresistance. If, on the other hand, the content exceeds 80% by weight,the adhesion strength under a high temperature decreases.

The particle diameter of the silicon carbide powder is between 0.01 μmand 100 μm, preferably, between 0.1 μm and 15 μm, and more preferablybetween 0.1 μm and 10 μm. If the particle diameter exceeds 100 μm, theadhesive force and thermal conductivity decrease. If the particlediameter is less than 0.01 μm, the cost of the sealing material layers15 a and 15 b increases.

The procedures for manufacturing the above mentioned ceramic filterassembly 9 will now be described.

First, a ceramic ingredient slurry used in an extrusion molding process,a sealing paste used in an end face sealing process, and a sealingmaterial layer forming paste used in a filter adhesion process areprepared in advance.

The ceramic ingredient slurry is formed by mixing and kneading apredetermined amount of silicon carbide powder, organic binder, andwater (in some cases, metal silicon is also added). The sealing paste isformed by mixing and kneading silicon carbide powder, organic binder,lubricant, plasticizer, and water. The sealing material layer formingpaste is formed by mixing and kneading predetermined amounts ofinorganic fibers, inorganic binder, organic binder, inorganic particles,and water.

Next, the ceramic ingredient slurry is charged into the extruder, and iscontinuously extruded through a metal mold die. The extruded honeycombmolded product is cut into equal lengths to obtain cut pieces of squarecolumnar honeycomb molded products. Further, a predetermined amount ofsealing paste is filled into an opening on one side of each cell of thecut piece to seal both end faces of each cut piece.

Subsequently, sintering temperature, sintering time and the like are setto a predetermined condition to perform main sintering, and thehoneycomb molded product cut piece and the plug 14 are completelysintered. To have the average pore diameter be 6 μm to 100 μm, and theporosity be 30% to 80%, the sintering temperature is set to 1400° C. to2300° C. in the present embodiment. The sintering time is set between0.1 hour and 5 hours. The atmosphere within the furnace during sinteringis inactive, and the pressure of the atmosphere is normal.

Next, after a base coating layer made of ceramic is formed on the outersurface of the honeycomb filter F1 if necessary, the sealing materiallayer forming paste is applied thereto. Then, 4 to 130 of such honeycombfilters F1 are used to adhere the outer surfaces of the honeycombfilters F1 with each other and integrate the honeycomb filters F1.

In the subsequent outer shape cutting process, unnecessary parts of theperipheral portion of the assembly 9 having a square cross sectionobtained through the filter adhering process is ground and removed, theceramic sealing material layer forming paste is applied to theperipheral portion to form an outer ceramic sealing material layer. Thisadjusts the outer shape. As a result, the ceramic filter assembly 9having a substantially elliptical cross section is manufactured.

The outer ceramic sealing material layer will now be described. Thethickness of a normal outer ceramic sealing material layer is uniform.In the present embodiment, as shown in FIG. 10( b), in the outer ceramicsealing material layer, the portion located along an extention of themajor axis of the assembly 9 is denoted by 15 c, the portion locatedalong an extension of the minor axis of the assembly 9 is defined as 15d, and the thickness of portion 15 c is denoted by H1, and the thicknessof portion 15 d is denoted by H2.

Depending on the type of assembly 9, the cell 12, or recesses, areexposed from the peripheral surface of the assembly 9 by the grindingprocess. In this case, the thickness of the ceramic sealing materiallayer is defined as the distance from a curve surface connecting thecell walls 13 a and 13 b of the exposed cells 12.

The ceramic sealing material layer forming paste is applied so that thethickness of the middle part between the portion 15 c and the portion 15d changes gradually. The adjustment of the thickness of the ceramicsealing material layer is possible by performing machining after theapplication of the paste. Alternatively, the sealing material layer maybe formed by injecting and drying the ceramic sealing material in themold so that the sealing material layer has such thickness.

The ratio H2/H1 is preferably 0.95 or less. If the ratio H2/H1 isgreater than 0.95, the filter in the long side direction easily cools,and uniform temperature rise of the assembly 9 becomes difficult. Thiscauses soot to remain and cracks tend to occur.

The ratio H2/H1 is preferably 0.06 or greater. If the ratio H2/H1 isless than 0.06, the release of heat reverses between the short sidedirection and the long side direction. Thus, a uniform temperature riseof the assembly 9 becomes difficult.

The assembly 9 is wrapped by the thermal insulation material 10 (referto FIG. 1 and FIG. 10( c)) and is accommodated in the casing 8. Thethermal insulation material normally has a uniform thickness. In thepresent embodiment, the thickness of the thermal insulation materialdiffers between portion 16 a, which is located along an extension of themajor axis of the assembly 9, and portion 16 b, which is located alongan extension of the minor axis of the assembly 9. In the followingdescription, the thickness of portion 16 a is denoted by I1, and thethicknessof portion 16 b is denoted by I2.

The ratio of I2/I1 is preferably 0.91 or less. If the ratio I2/I1 isgreater than 0.91, the filters F1 near the outer side in the directionof the long side cools easily, uniform temperature rise of the assembly9 becomes difficult, and soot remains thereby causing cracks to easilyoccur. It is preferable that the ratio I2/I1 be 0.30 or greater. If theratio I2/I1 is less than 0.30, the heat release reverses between theshort side direction and the long side direction and thus uniformtemperature rise of the assembly 9 becomes difficult.

For the thermal insulation material 10, a mat formed from typicalceramic fibers, alumina fibers, and alumina silicate fibers may be used.

The fine particle trapping effect of the ceramic filter assembly 9 willnow be briefly described.

Exhaust gas, which is supplied from the upstream side end face 9α of theceramic filter assembly 9, flows into the cells 12 that are opened inthe upstream side end face 9α. The exhaust gas passes through the cellwalls 13 a and 13 b and reaches the interior of the cells 12 opened inthe adjacent downstream end face 9β. The gas that passes through thewalls 13 a and 13 b flows out from the downstream side end face 9β ofthe honeycomb filter F1 through the opening of the corresponding cells12. The fine particles contained in the exhaust gas does not passthrough the cell walls 13 a and 13 b and become trapped in the walls 13a and 13 b. And, the gas from which the fine particles are removed(purified gas) is discharged from the downstream side end face 9β of thehoneycomb filter F1. The purified gas passes through the second exhaustpipe 7 and is released into the atmosphere. The trapped fine particlesare ignited and burned by the action of the above mentioned catalystwhen the internal temperature of the assembly 9 reaches a predeterminedtemperature.

A thermal shock test conducted on the filter will now be described.

[Test 1]

First, 51.5% by weight of α-silicon carbide powder having an averageparticle diameter of 10 μm and 22% by weight of β-silicon carbide powderhaving an average particle diameter of 0.5 μm were wet mixed, and 6.5%by weight of organic binder (methyl cellulose) and 20% by weight ofwater were added to the obtained mixture and kneaded. Next, a smallamount of plasticizer and lubricant were added to the kneaded mixtureand was further kneaded, and was then extruded with a different metalmold die to obtain a honeycomb molded product.

Subsequently, after drying the molded product with a microwave drier,the cells (through holes) of the molded product were sealed with thesealing paste made of a porous silicon carbide sintered material. Then,the drier was used again to dry the sealing paste. Subsequently, thedried body was degreased at 400° C., and then baked for about 3 hours at2200° C. under an argon atmosphere of normal pressure. As a result, ahoneycomb filter F1 made of porous silicon carbide sintered body wasobtained. In accordance with this method, a filter having a dimension asshown in table 1 was prepared. The length of each filter was unified to150 mm.

Each filter was gradually heated to 600° C. or 800° C. in an electricfurnace, and was held for 3 hours at a target temperature. Thereafter,the filter was placed under a normal temperature of 20° C. to applythermal shock to the filter. The occurrence of cracks is shown in table1.

With the thermal shock of 600° C. and 800° C., cracks occurred when theratio B1/B2 was 3.04 or greater. It was found that a filter cansufficiently withstand a thermal shock of about 800° C., at which it maybe used, when the ratio B1/B2 is 3.0 or less.

[Test 2]

First, 51.5% by weight of silicon carbide powder having an averageparticle diameter 10 μm, 12% by weight of silicon carbide powder havingan average particle diameter of 0.5 μm, and 10% by weight of metalsilicon having an average particle diameter of 0.5 μm were wet mixed,and 6.5% by weight and 20% by weight of the organic binder (methylcellulose) and water were each added to the obtained mixture andkneaded. Next, a small amount of plasticizer and lubricant were added tothe kneaded mixture and was further kneaded, and was then extruded witha different metal mold die to obtain a honeycomb molded product.

Subsequently, after drying the molded product with a microwave drier,the cells (through holes) of the molded product were sealed with thesealing paste made of a porous silicon carbide sintered material. Thedrier was used again to dry the sealing paste. Subsequently, the driedbody was degreased at 400° C., and then baked for about 3 hours at 1500°C. under an argon atmosphere of normal pressure. As a result, ahoneycomb filter F1 made of porous silicon carbide-metal siliconsintered material was obtained. In accordance with this method, filtershaving the dimensions shown in table 2 were prepared. The length of eachfilter was unified to 150 mm. In the same manner as test 1, a thermalshock test was conducted. As shown in table 2, with a thermal shock of600° C., cracks occurred when the ratio B1/B2 was 3.09 or greater. Inthe thermal shock of 800° C., cracks occurred when the ratio B1/B2 was3.04 or greater. It was found that a filter can sufficiently withstand athermal shock of about 800° C., at which it is used, when the ratioB1/B2 is 3.0 or less.

[Test 3]

In test 3, filters were manufactured through the same procedure as intest 1. However, the inner diameter of the cells (through holes) waschanged. The result of the dimensions and the thermal shock test isshown in table 3. It is apparent from the result that with a thermalshock of 600° C. and 800° C., cracks occurred when the ratio C1/C2 was3.07 or greater. It was found that a filter can sufficiently withstand athermal shock of about 800° C., at which it is used, when the ratioC1/C2 is equal 3.0 or less.

[Test 4]

In test 4, filters were manufactured through the same procedure as intest 2. However, the inner diameter of the cells (through holes) waschanged. The result of the dimensions and the thermal shock test isshown in table 4. It is apparent from the result that with a thermalshock of 600° C., cracks occurred when the ratio C1/C2 was 3.20 orgreater, and with a thermal shock of 800° C., cracks occurred when theratio C1/C2 was 3.07 or greater. It was found that a filter cansufficiently withstand a thermal shock of about 800° C., at which it isused, when the ratio C1/C2 is 3.0 or less.

[Test 5]

In test 5, filters were manufactured through the same procedure as intest 1. However, the wall thickness was changed. The result of thedimensions and the thermal shock test is shown in table 5. It isapparent from the result that with thermal shock of 600° C. and 800° C.,cracks occurred when the ratio D1/D2 was 3.03 or greater. It was foundthat a filter can sufficiently withstand the thermal shock of about 800°C., at which it is used, when the ratio D1/D2 is 3.0 or less.

[Test 6]

In test 6, filters were manufactured through the same procedure as intest 2. However, the wall thickness was changed. The dimensions and theresults of the thermal shock are shown in table 6. It is apparent fromthe results that with thermal shock of 600° C., cracks occurred when theratio D1/D2 was 3.08 or greater, and with thermal shock of 800° C.,cracks occurred when the ratio D1/D2 was 3.03 or greater. It was foundthat a filter can sufficiently withstand a thermal shock of about 800°C., at which it is used, when the ratio D1/D2 is 3.0 or less.

EXAMPLES AND COMPARATIVE EXAMPLES Example 1-1

First, 51.5% by weight of α-silicon carbide powder and 22% by weight ofβ-silicon carbide powder were wet mixed, and 6.5% by weight of anorganic binder (methyl cellulose) and 20% by weight of water were addedto the obtained mixture and kneaded. Next, a small amount of plasticizerand lubricant were added to the kneaded mixture and was further kneaded,and was then extruded with a different metal mold die to obtain ahoneycomb molded product.

Subsequently, after drying the molded product with a microwave drier,the cells (through holes) 12 of the molded product were sealed with thesealing paste made of a porous silicon carbide sintered material. Then,the drier was used again to dry the sealing paste. Subsequently, thedried body was degreased at 400° C., and was then baked for about 3hours at 2200° C. under an argon atmosphere at normal pressure. As aresult, honeycomb filters F1 made from the porous silicon carbidesintered material were obtained. In each honeycomb filter, the long sideB1 was set to 66.9 mm, the short side B2 was set to 32.7 mm, the lengthL was set to 150 mm, both lengths of the long side and the short side ofthe cells 12 were set to 1.5 mm, and both thicknesses D1 and D2 of thecell walls 13 a and 13 b were set to 0.3 mm (in the same manner as intest example 1.2).

Then, 23.3% by weight of ceramic fibers, 30.2% by weight of siliconcarbide powder having an average particle diameter of 0.3 μm, 7% byweight of silica sol serving as the inorganic binder, 0.5% by weight ofcarboxymethyl cellulose serving as the inorganic binder, and 39% byweight of water were mixed and kneaded. By adjusting such kneadedmixture to an appropriate viscosity, the paste used for forming thesealing material layers 15 a, 15 b, and 15 c was prepared. The ceramicfibers were alumina silicate ceramic fibers having a shot content of 3%with fiber lengths of 0.1 mm to 100 mm, and the conversion amount ofsilica sol in terms of SiO₂ amount was 30%.

The sealing material layer forming paste was then uniformly applied tothe outer surfaces of the honeycomb filters F1 to form the sealingmaterial layers 15 a and 15 b with a thickness of 1.0 mm. Nine honeycombfilters F1 were arranged in the same direction in three rows and threecolumns and dried for 1 hour at 100° C. with the outer surfaces adheredto each other. The sealing material layers 15 a and 15 b were thencured, and the nine honeycomb filters F1 were integrated. The outershape cutting process was performed to form an ellipse with the crosssectional shape of the assembly of the integrated nine honeycomb filtersF1. The major axis A1 of the ellipse was 160 mm, the minor axis A2 was80 mm, and the ratio A1/A2 was 2. The sealing material layer 15 c havinga thickness of 1.5 mm was applied to the peripheral portion of theassembly and the outer shape was cut and trimmed to manufacture aceramic filter assembly 9 a having a substantially elliptical crosssection, as shown in FIG. 6( a).

The thermal insulation material 10 was uniformly wrapped around theassembly 9 a that was obtained as described above to a thickness of 10mm. The assembly 9 a was accommodated in the casing 8, and the exhaustgas was actually supplied. As shown in FIG. 3( a), a thermocouple wasembedded at one location P(Temp.) at substantially the center of thehoneycomb filter F1, and the temperatures Tα, Tβ, and Tγ of thehoneycomb filter F1 at three locations denoted by α, β, and γ in FIG. 6(a) were measured with time. Tα is the temperature at the center of afilter, Tβ is the temperature at a position 5 mm from the outermostsurface of the filter in the direction of the minor axis, and Tγ is thetemperature 5 mm from the outermost surface of the filter in thedirection of the major axis. The maximum temperature differences ΔT (°C.) between the positions α, β, and γ were also measured. The blackarrow in FIG. 3 shows the direction of the flow of the exhaust gas.

After repeating the reproduction test for a number of times (10 times),the assembly 9 was taken out and each honeycomb filter F1 was visuallyobserved to study the residual soot and the occurrence of cracks. As aresult, in example 1, the maximum temperature difference ΔT (° C.) wasapproximately 50° C., the value of which is extremely small. Further, noresidual soot was present in any of the honeycomb filters F1, and theoccurrence of cracks was not confirmed.

Comparative Examples 1-1 to 1-2

In comparative examples 1-1 and 1-2, the assembly 9 was manufacturedbasically in the same manner as in example 1-1. However, in comparativeexample 1-1, the long side B1 of each honeycomb filter F1 was changed to32.7 mm, the short side B2 was changed to 32.7 mm, and the length L waschanged to 150 mm (in the same manner as in test reference example 1.1(table 1)). Nine filters were arranged in three rows and three columnswith the long side B1 parallel to each other to manufacture the assembly9 b with a circular cross section of diameter 80 mm, as shown in FIG. 6(b). In comparative example 1-2, the long side B1 of each honeycombfilter F1 was changed to 32.7 mm, the short side B2 was changed to 32.7mm, and the length L was changed to 150 mm (in the same manner as intest reference example 1.1 (table 1). Fifteen filters were arranged inthree rows and five columns with the long side B1 parallel to each otherto manufacture assembly 9 c with a substantially elliptical crosssection (160 mm×80 mm), as shown in FIG. 6( c).

The same test as in example 1-1 was performed on the two types ofassemblies 9 b and 9 c. As a result, in comparative example 1-1, themaximum temperature difference ΔT(° C.) was about 50° C., which value isan extremely small value. No residual soot was present in any of thehoneycomb filters F1, the occurrence of cracks was not confirmed.

However, in comparative example 1-2, ΔT was approximately 100° C., thevalue of which is very large. Further, residual soot was present and theoccurrence of cracks was confirmed in the honeycomb filter F1 located atposition γ.

In the same manner, a similar test was performed on the siliconcarbide-metal silicon filter with respect to the maximum temperaturedifference ΔT(° C.) and the occurrence of cracks.

More specifically, in example 1-2, the assembly in which the filters oftest example 2.2 (table 2) were assembled as shown in FIG. 6( a) wasused. In comparative example 1-3, the assembly in which the filters oftest comparative example 2.1 were assembled as shown in FIG. 6( b) wasused. In comparative example 1-4, the assembly in which the filters oftest comparative example 2.1 were assembled as shown in FIG. 6( c) wasused.

As shown in table 7, the maximum temperature difference ΔT(° C.) was 60°C. in example 1-2, whereas in comparative example 1-4, the temperaturedifference was 110° C. or greater, and cracks were conformed in thehoneycomb filter at position γ.

Examples 2-1 to 2-4

In examples 2-1 to 2-4, the assembly 9 was manufactured basically in thesame manner as in comparative examples 1-3. In example 2-1, in the cells12 of each honeycomb filter F1, C1 was set to 1.7 mm and C2 was set to1.5 mm. Therefore, C1/C2=1.13. Five honeycomb filters F1 were arrangedparallel to the long side of the cell 12, and three honeycomb filters F1were arranged perpendicular to the long side of the cells 12 to assemblean assembly of fifteen honeycomb filters F1. The outer shape cuttingprocess was performed to manufacture an assembly 9 d (160 mm×80 mm×150mm) having a substantially elliptical cross section, as shown in FIG. 7(a). As shown in table 8, examples 2-2 to 2-4 differ from example 2-1only in the dimensions of the cells 12.

Comparative Examples 2-1 to 2-4

The assembly 9 was also manufactured basically in the same manner as inexample 2-1 in comparative examples 2-1 to 2-4. However, in comparativeexample 2-1, the dimension C1 of the cell 12 was 1.5 mm, C2 was 1.5 mm,and C1/C2=1. After assembling the honeycomb filters F1 in three rows andfive columns, the outer shape cutting was performed to manufacture anassembly 9 e (160 mm×80 mm×150 mm) having a substantially ellipticalcross section, as shown in FIG. 7(b). In comparative example 2-2, thedimension C1 of the cell 12 was 1.5 mm, C2 was 1.7 mm, and C1/C2=0.88.Fifteen honeycomb filters F1 were assembled by arranging five sets ofthe filters F1 parallel to the 1.5 mm side with three filters F1arranged vertically in each set. The outer shape cutting was performedto manufacture assembly 9 f (160 mm×80 mm×150 mm) having a substantiallyelliptical cross section, as shown in FIG. 7( c). The comparativeexample 2-3 was manufactured in the same manner as in comparativeexample 2-2, and comparative example 2-4 was manufactured in the samemanner as in example 2-1.

With respect to the assemblies of examples 2-1 to 2-4, and comparativeexamples 2-1 to 2-4, the maximum temperature difference ΔT and theoccurrence of cracks were studied. As a result, the maximum temperaturedifference ΔT (° C.) was 93° C. or less in examples 2-1 to 2-4, and noresidual soot was present in any of the honeycomb filters F1, and theoccurrence of cracks was not confirmed.

However, in comparative example 2-1, comparative example 2-2, andcomparative example 2-3, the maximum temperature difference ΔT (° C.)was greater than or equal to 100° C., the value of which is very large.Residual soot was present and the occurrence of cracks was confirmed inthe honeycomb filter F1 at position γ. Further, in comparative example2-4, the temperature difference was low but cracks occurred.

Examples 2-5 to 2-8, Comparative Examples 2-5 to 2-8

In the same manner, the maximum temperature difference ΔT (° C.) and theoccurrence of cracks in the silicon carbide-metal silicon filter werestudied.

More specifically, in examples 2-5 to 2-8, the filters of test examples4.1 to 4.4 (table 4) were used in a state assembled as shown in theassembly of FIG. 7( a). In comparative example 2-5, the filters of thetest reference example 4.1 were used in a state assembled as shown inFIG. 7( b). In comparative examples 2-6, 2-7, the filters of testexamples 4.1 and 4.2, were used in a state assembled as shown in theassembly of FIG. 7( c). In comparative example 2-8, the filters of testcomparative example 4.1 were used in a state assembled as shown in theassembly of FIG. 7( a).

The maximum temperature difference ΔT (° C.) of examples 2-5 to 2-8 was110° C. or less, whereas the maximum temperature difference ΔT (° C.) ofcomparative examples 2-5 to 2-8 was 110° C. or greater, and cracksoccurred in the honeycomb filter located at position γ.

The results are shown in table 8.

Examples 3-1 to 3-4

In examples 3-1 to 3-4, the assembly 9 was manufactured basically in thesame manner as in comparative example 1-3. However, in example 3-1, thedimension D1 of the cell wall 13 of each honeycomb filter F1 was changedto 0.4 mm, and D2 was changed to 0.35 mm. Therefore, D1/D2=1.14. Fivehoneycomb filters F1 were arranged parallel to D1 and three honeycombfilters F1 were arranged perpendicular to D1 to form an assembly offifteen honeycomb filters F1. The outer shape cutting process wasperformed to manufacture an assembly 9 g (160 mm×80 mm×150 mm) having asubstantially elliptical cross section, as shown in FIG. 8( a). In thesame manner, the assembly of examples 3-2 to 3-4 were manufactured.

Comparative Examples 3-4l to 3-4

The assembly was also manufactured basically in the same way as inexample 3-1 in comparative examples 3-1 to 3-4. However, in comparativeexample 3-1, the dimension D1 was changed to 1.5 mm, and D2 was changedto 1.5 mm. Therefore, ratio D1/D2=1. After assembling the honeycombfilters F1 in three rows and five columns, the outer shape cuttingprocess was performed to manufacture an assembly 9 h (160 mm×80 mm×150mm) having a substantially elliptical cross section, as shown in FIG. 8(b). In comparative example 3-2, the dimension D1 was 0.35 mm, and D2 was0.4 mm. Therefore, ratio D1/D2=0.88. Five of such honeycomb filters F1were arranged parallel to D2 and three honeycomb filters F1 werearranged perpendicular to D2 to form an assembly of fifteen honeycombfilters F1. The outer shape cutting process was performed to manufacturean assembly 9 i (160 mm×80 mm×150 mm) having a substantially ellipticalcross section, as shown in FIG. 8( c). The comparative example 3-3 wasmanufactured in the same manner as in comparative example 3-2, andcomparative example 3-4 was manufactured in the same manner as inexample 3-1.

With respect to the assembly of examples 3-1 to 3-4, and comparativeexamples 3-1 to 3-4, the maximum temperature difference ΔT and theoccurrence of cracks were studied. As a result, as shown in table 9, themaximum temperature difference ΔT (° C.) was 91° C. or less in examples3-1 to 3-4. Further, no residual soot was present and the occurrence ofcracks was not recognized in any of the honeycomb filters F1.

However, in comparative example 3-1, comparative example 3-2, andcomparative example 3-3, the maximum temperature difference ΔT (° C.)was greater than or equal to approximately 95° C., the value of which isvery large. Further, residual soot was present and the occurrence ofcracks was confirmed in the honeycomb filter F1 at position γ. Further,in comparative example 3-4, the temperature difference was low butcracks occurred.

Examples 3-5 to 3-8, Comparative Examples 3-5 to 3-8

In the same manner, similar tests were performed on a siliconcarbide-metal silicon filter.

More specifically, in examples 3-5 to 3-8, an assembly formed byarranging the filters of test examples 6.1 to 6.4 (table 6), as shown inFIG. 8( a), was used. In comparative example 3-5, an assembly formed byarranging the filters of the test reference example 6.3, as shown inFIG. 8( b), was used. In comparative example 3-6 and comparative example3-7, assemblies formed by arranging the filters of test examples 6.1 and6.4 (table 6), respectively, as shown in FIG. 8( c), were used. Incomparative example 3-8, an assembly formed by arranging the filters oftest comparative example 6.1, as shown in FIG. 8( a) was used.

As shown in table 9, the maximum temperature difference of examples 3-5to 3-8 was 101° C. or less. In comparison, in comparative examples 3-5,3-6, and 3-7, the maximum temperature difference was 105° C. or greater,and cracks occurred in the honeycomb filter located at position γ. Incomparative example 3-8, the temperature difference was low, but cracksoccurred.

Examples 4-1 to 4-5, Comparative Examples 4-1 to 4-3

In examples 4-1 to 4-5, an assembly 9 was manufactured basically in thesame manner as in comparative example 1-2 using the filters of the testreference example 1.1 (table 1). In example 4-1, however, the thicknessE1 of the sealing material layer 15 a was 1.05 mm, the thickness E2 ofthe sealing material layer 15 b was 1 mm, and the ratio E1/E2=1.05(refer to FIG. 9( a)).

Similarly, example 4-2 to example 4-5 and comparative example 4-3 weremanufactured in accordance with the description of table 10.

In comparative example 4-1, the thickness E1 of the sealing materiallayer 15 a was 1 mm, the thickness E2 of the sealing material layer 15 bwas 1 mm, and E1/E2=1 (refer to FIG. 9( b)).

In comparative example 4-2, the assembly was manufactured basically inthe same manner as in comparative example 1-2 using the filters of testreference example 1.1. In example 4-2, however, the thickness E1 of thesealing material layer 15 a was 1 mm, the thickness E2 of the sealingmaterial layer 15 b was 2 mm, and the ratio E1/E2=0.5 (refer to FIG. 9(c).).

With respect to the assemblies of examples 4-1 to 4-5 and comparativeexamples 4-1 to 4-3, the maximum temperature difference Tβ-Tα and theoccurrence of cracks were studied. As a result, as shown in table 10,the maximum temperature difference Tβ-Tα was 75° C. or less in examples4-1 to 4-5, and no residual soot was present and the occurrence ofcracks was not confirmed in any of the honeycomb filters F1.

However, in comparative example 4-1 and comparative example 4-2, themaximum temperature difference Tβ-Tα was greater than or equal to 80°C., the value of which is very large, and residual soot was present andthe occurrence of cracks was confirmed in the honeycomb filter F1located at position γ. Further, in comparative example 4-3, thetemperature difference was reversed and cracks occurred at position β.

Examples 4-6 to 4-10, Comparative Examples 4-4 to 4-6

In the same manner, similar tests were performed on a siliconcarbide-metal silicon filter.

In example 4-6 to example 4-10, an assembly was manufactured basicallyin the same manner as in comparative example 1-2 using the filter of thetest reference example 2.1. In example 4-6, however, the thickness ofthe sealing material layer parallel to the long side of the assembly 9was E1 (1.05 mm), and the thickness of the sealing material layerparallel to the short side was E2 (1 mm), and thus E1/E2=1.05.

Similarly, example 4-6 to example 4-10 and comparative example 4-6 weremanufactured in accordance with table 10.

In the assembly of comparative example 4-4, the thickness E1 of thesealing material layer 15 a was 1 mm, the thickness E2 of the sealingmaterial layer 15 b was 1 mm and thus E1/E2=1 (refer to FIG. 9( b)).

In comparative example 4-5, the assembly was manufactured basically inthe same manner as in comparative example 1-2 using the filter of testreference example 2.1. In example 4-5, however, the thickness E1 of thesealing material layer 15 a was 1 mm, the thickness E2 of the sealingmaterial layer 15 b was 2 mm, and the ratio E1/E2=0.5 (refer to FIG. 9(c)).

With respect to the assembly of examples 4-6 to 4-10 and comparativeexamples 4-4 to 4-6, the maximum temperature difference Tβ-Tα and theoccurrence of cracks were studied. As a result, as shown in table 10,the maximum temperature difference Tβ-Tα was 80° C. or less in theexamples, and no residual soot was present and the occurrence of crackswas not confirmed in any of the honeycomb filters F1.

However, in comparative example 4-4 and comparative example 4-5, themaximum temperature difference Tβ-Tα was greater than or equal to 100°C., the value of which is very large, residual soot was present and theoccurrence of cracks was confirmed in the honeycomb filter F1 located atposition γ. Further, in comparative example 4-6, the temperaturedifference was reversed and cracks occurred at position β.

Examples 5-1 to 5-4, Comparative Examples 5-1 to 5-3

In examples 5-1 to 5-4, an assembly was manufactured basically in thesame manner as in comparative example 1-2 using the filter of testreference example 1.1 (table 1). In example 5-1, however, the thermalconductivity G1 of the sealing material layer 15 a was 0.2 W/m·K, thethermal conductivity G2 of the sealing material layer 15 b was 0.3W/m·K, and G1/G2=0.67 (refer to FIG. 10( a)).

Similarly, in example 5-2 to example 5-4 and comparative examples 5-1 to5-3, assemblies were manufactured by adjusting G1 in accordance with thedescription of table 11.

In comparative example 5-1, G1 and G2 were the same and thus G1/G2=1.

With respect to the assemblies of examples 5-1 to 5-4 and comparativeexamples 5-1 to 5-3, the maximum temperature difference Tβ-Tα and theoccurrence of cracks were studied. As a result, as shown in table 11,the maximum temperature difference Tβ-Tα was 76° C. or less in examples5-1 to 5-4, and no residual soot was present and the occurrence ofcracks was not confirmed in any of the honeycomb filters F1.

However, in comparative example 5-1 and comparative example 5-2, themaximum temperature difference Tβ-Tα was greater than or equal to 80°C., the value of which is very large, and residual soot was present andthe occurrence of cracks were confirmed in the honeycomb filter F1located at position γ. Further, in comparative example 5-3, thetemperature difference was reversed and cracks occurred at position β.

Examples 5-5 to 5-8, Comparative Examples 5-4 to 5-6

In the same manner, similar tests were performed on a siliconcarbide-metal silicon filter.

In example 5-5 to example 5-8 and comparative example 5-4 to comparativeexample 5-6, an assembly was basically manufactured in accordance withthe description of table 11 using the filter of test reference example2.1.

In examples 5-5 to 5-8, the temperature difference Tβ-Tα was 80° C. orless, and no residual soot was present and the occurrence of cracks wasnot confirmed in any of the honeycomb filters F1.

However, in comparative example 5-4 and comparative example 5-5, themaximum temperature difference Tβ-Tα was greater than or equal to 80°C., the value of which is very large, and residual soot was present andthe occurrence of cracks was confirmed in the honeycomb filter F1located at position γ. Further, in comparative example 5-6, thetemperature difference was reversed and cracks occurred at position β.

The results are shown in table 11.

Example 6-1 to 6-4, Comparative Example 6-1 to 6-3

In examples 6-1 to 6-4, an assembly was manufactured basically in thesame manner as in comparative example 1-2 using the filter of testreference example 1.1. In example 6-1, however, the thickness Hi of theouter sealing material layer 15 c was 1.6 mm, thickness H2 of the outersealing material layer 15 d was 1.5 mm, and thus H2/H1=0.94 (refer toFIG. 10( b)). The thickness between the outer sealing material layers 15c and 15 d was adjusted so that the thicknesses of the outer sealingmaterial layers were gradually changed. Therefore, the thicknesses H1and H2 were either the maximum thickness or the minimum thickness of theouter sealing material layer.

Similarly, the assembly of example 6-2 to example 6-4, and comparativeexamples 6-1 to 6-3 were manufactured by adjusting the thickness of H2in accordance with the description of table 12.

In comparative example 6-1, H2/H1=1.

As shown in table 12, in examples 6-1 to 6-4, the maximum temperaturedifference Tβ-Tα was 73° C. or less and no residual soot was present andthe occurrence of cracks was not confirmed in any of the honeycombfilters F1.

However, in comparative example 6-1 and comparative example 6-2, themaximum temperature-difference Tβ-Tα was 80° C. or greater, the value ofwhich is very large, and residual soot was present and the occurrence ofcracks was confirmed in the honeycomb filter F1 located at position γ.Further, in comparative example 6-3, the temperature difference wasreversed and cracks occurred at position β.

Examples 6-5 to 6-8, Comparative Examples 6-4 to 6-6

In the same manner, similar tests were performed on a siliconcarbide-metal silicon filter.

Example 6-5 to example 6-8 and comparative example 6-4 to comparativeexample 6-6 were basically manufactured in accordance with thedescription of table 12 using the filter of the test reference example2.1.

As shown in table 12, in examples 6-5 to 6-8, the temperature differenceTβ-Tα was 80° C. or less. Further, no residual soot was present and theoccurrence of cracks was not confirmed in any of the honeycomb filtersF1.

However, in comparative example 6-4 and comparative example 6-5, themaximum temperature difference Tβ-Tα was greater than or equal to 83°C., the value of which is very large. Further, residual soot was presentand the occurrence of cracks was confirmed in the honeycomb filter F1located at position γ. Further, in comparative example 6-6, thetemperature difference was reversed and cracks occurred at the positionof β.

Examples 7-1 to 7-3, Comparative Examples 7-1 to 7-3

In examples 7-1 to 7-3, an assembly was manufactured basically in thesame manner as in comparative example 1-2 using the filter of testreference example 1.1. In example 7-1, however, the thickness I1 ofportion 16 a of the outer thermal insulation material (mat made ofalumina fiber) was 10 mm, the thickness I2 of portion 16 b was 11 mm,and I2/I1=0.91 (refer to FIG. 10( c)). The thickness between portion 16a and 16 b was adjusted so that the thickness of the thermal insulationmaterial 10 was gradually changed. Therefore, the thicknesses H1 and H2were either the maximum thickness or the minimum thickness of thethermal insulation material.

In the same manner, example 7-2 to example 7-3 and comparative example7-3 were manufactured by adjusting the thickness of I2 in accordancewith the description of table 13.

In comparative example 7-1, I1 and I2 had the same thickness as inH2/H1=1.

As shown in table 13, in examples 7-1 to 7-8, the maximum temperaturedifference Tβ-Tα was 73° C. or less. Further, no residual soot waspresent and the occurrence of cracks was not recognized in any of thehoneycomb filters F1.

However, in comparative example 7-1 and comparative example 7-2, themaximum temperature difference Tβ-Tα was greater than or equal to 80°C., the value of which is very large. Further, the residual soot waspresent and the occurrence of cracks was confirmed in the honeycombfilter F1 located at position γ. Further, in comparative example 7-3,the temperature difference was reversed and cracks occurred at positionβ.

Examples 7-4 to 7-6, Comparative Examples 7-4 to 7-6

In the same manner, similar tests were performed on a siliconcarbide-metal silicon filter.

Example 7-4 to example 7-6 and comparative example 7-4 to comparativeexample 7-6 were basically manufactured in accordance with thedescription of table 13 using the filter of test reference example 2.1.

The temperature difference Tβ-Tα was 80° C. or less in examples 7-4 to7-6. Further, no residual soot was present and the occurrence of crackswas not confirmed in any of the honeycomb filters F1.

However, in comparative example 7-4 and comparative example 7-5, themaximum temperature difference Tβ-Tα was greater than or equal to 83°C., the value of which is very large. Further, residual soot was presentand the occurrence of cracks was confirmed in the honeycomb filter F1located at position γ. Further, in comparative example 7-6, thetemperature difference was reversed and cracks occurred at position β.

The present embodiment has the advantages described below.

(1) The assembly 9 is manufactured by adhering a plurality of ceramicfilters F1 so that the long sides of ceramic filters F1 havingrectangular cross sections extend in the direction of the major axis ofthe assembly 9 and the short sides of the ceramic filters F1 extend inthe direction of the minor axis of the assembly 9. Thus, in the majoraxis direction of the assembly 9, the number of ceramic sealing materiallayers 15 b that may influence thermal conductivity is reduced.Therefore, the thermal conductivity in the major axis direction ishigher than the thermal conductivity in the minor axis direction of theassembly 9 during use, and the filters F1 at the peripheral portion inthe major axis direction are more easily heated. The residual soot isthus not present and cracks do not occur. Further, this may be achievedby changing the ceramic structure without changing the material of theceramic filter thereby reducing costs.

Further, in such a method, when a hypothetical first straight lineintersects the generally elliptical contour at two points in which thedistance therebetween is maximum and a hypothetical second straight lineorthogonal to the first straight line intersects the generallyelliptical contour at two points in which the distance therebetween isminimum, the number of sealing material layers the second straight lineof the assembly traverses is less than or equal to the number of sealingmaterial layers and first straight line traverses. This reduces thermalconduction obstacles between filters.

(2) The rectangular cells 12 in the columnar honeycomb filters F1produce a deviation of thermal conduction in the cross section of thefilter. That is, the thermal conductivity in the long side direction ofeach cell is higher than the thermal conductivity in the short sidedirection of the cell. The assembly may be formed by arranging the cellsso that their long sides are parallel to the major axis direction of andtheir short sides are parallel to the minor axis direction of theassembly. This results in the thermal conductivity in the major axisdirection being greater than the thermal conductivity in the minor axisdirection of the assembly during use. Further, the filters F1 at theperipheral portion in the major axis direction are more easily heated.Thus, residual soot is eliminated and cracks do not occur. Further, thisis easily achieved by changing the ceramic structure without changingthe material of the ceramic filter. Thus, costs are reduced.

(3) The cells 12 in the columnar honeycomb filter F1 are rectangular. Bychanging the thicknesses of cell walls that are orthogonal to eachother, deviation of the thermal conductivity may be produced along thecross section of the filter. That is, the thermal conductivity in thedirection in which the thick cell walls extend is higher than thethermal conductivity in the direction in which the thin cell wallsextend. The filter assembly may be formed so that the major axisdirection of the assembly is parallel to the direction in which thethick cell walls extend and the minor axis direction of the assembly isparallel to the direction in which the thin cell walls extend. Thisresults in the thermal conductivity in the major axis direction beinghigher than the thermal conductivity in the minor axis direction of theassembly during use. Further, the filters F1 at the peripheral portionin the major axis direction are more easily heated. Thus, residual sootis eliminated and cracks do not occur. Further, this is easily achievedby changing the ceramic structure without changing the material of theceramic filter. Thus, costs are reduced.

(4) By making the sealing material layers 15 b, which are perpendicularto the major axis direction, relatively thin, the thermal conductivityin the major axis direction becomes higher than the thermal conductivityin the minor axis direction of the assembly 9. Thus, the filters F1 atthe peripheral portion in the major axis direction are more easilyheated, residual soot is eliminated, and cracks do not occur. Further,this is easily achieved by changing the ceramic structure withoutchanging the material of the ceramic filter. Thus, costs are reduced.

(5) By changing the thermal conductivity G2 of the sealing materiallayers 15 b, which are perpendicular to the major axis direction, to ahigh value, the thermal conductivity in the major axis direction becomeshigher than in the minor axis direction of the assembly during use.Thus, the filters F1 at the peripheral portion in the major axisdirection are more easily heated, residual soot is eliminated, andcracks do not occur. Further, this is easily achieved by changing theceramic structure without changing the material of the ceramic filter.Thus, costs are reduced.

(6) In the ceramic filter assembly having a generally elliptical crosssection, with regards to the outer sealing *material layer, whichinhibits thermal conduction, the thickness Hi of the sealing materiallayer located along an extension of the major axis is greater than thethickness H2 of the sealing material layer located along an extension ofthe minor axis to suppress heat radiation from the peripheral portion inthe major axis direction. This produces a high thermal insulation effectat the peripheral portion in the major axis direction. Thus, residualsoot is eliminated, and cracks do not occur. Further, this is easilyachieved by changing the ceramic structure without changing the materialof the ceramic filter. Thus, costs are reduced.

(7) In the ceramic filter assembly 9 having a generally elliptical crosssectional shape, with regards to the thickness of the thermal insulationmaterial 10 that inhibits thermal conduction, the thickness I1 ofportion 16 a located along an extension of the major axis is greaterthan the thickness I2 of portion 16 b located along an extension of theminor axis. This suppresses heat radiation from the peripheral portionin the major axis direction. Thus, a high thermal insulation effect isproduced at the peripheral portion in the major axis direction duringuse of the assembly. Thus, residual soot is eliminated, and cracks donot occur. Further, this is easily achieved by changing the ceramicstructure without changing the material of the ceramic filter. Thus,costs are reduced.

(8) According to tests 1 and 2, when the cross sectional shape of acolumnar honeycomb filter made of a porous ceramic sintered body isrectangular and the length of the long side is B1 and the length of theshort side is B2, if the ratio B1/B2 is 3.0 or less, cracking due tothermal shock is less likely to occur. Thus, thermal shock resistance isconsidered to be about the same as when the cross sectional shape issquare, and a filter unit necessary for a uniform temperature rise ofthe flat shape filter assembly 9 is provided. Since the sealing materialand the like may be reduced, costs are also reduced.

(9) According to tests 3 and 4, when the cross sectional shape of a cell(through hole) of a columnar honeycomb filter made of porous ceramicsintered body is rectangular and the length of the long side is C1 andthe length of the short side is C2, if the ratio C1/C2 is 3.0 or less,cracking due to thermal shock is less likely to occur. Thus, the thermalshock resistance is considered to be about the same as when the crosssectional shape of the cell (through hole) is square, and a filter unitnecessary for a uniform temperature rise of the flat shaped filterassembly 9 is provided.

(10) According to tests 5 and 6, when there are two wall thicknesses fora cell of a columnar honeycomb filter made of porous ceramic sinteredbody and the dimension of the thick wall is D1 and the dimension of thethin wall is D2, if the ratio D1/D2 is 3.0 or less, cracking due tothermal shock is less likely to occur. Thus, the thermal shockresistance is considered to be about the same as when all of the wallthicknesses are the same, and a filter unit necessary for a uniformtemperature rise of the oblong filter assembly 9 is provided.

The embodiment of the present invention may be modified in the followingway.

The cross sectional shape of the honeycomb filters F1 may berectangular, and the inner cells 12 may be rectangular in the samedirection.

The cross sectional shape of the honeycomb filters F1 may berectangular, and the thicker wall 13 a of the inner cell walls 13 a, 13b may be rectangular in the same direction as the long side.

Each cell of the honeycomb filter may be rectangular and the cell wallof the long side may be thicker than the cell wall of the short side.

The sealing material layer formed on the outer peripheral face of theassembly may be formed using two or more types of coating materials,which are applied to the outer surface, having different thermalconductivity.

The thermal insulation material 10 may be formed on the peripheralsurface of the assembly using two or more types of thermal insulationmaterials having different thermal conductivity.

TABLE 1 wall side length thickness cell outer outer (mm) (mm) pitchcolumn dimension (mm) dimension (mm) thermal shock test C1, C2 D1, D2(mm) number B1 B2 B1/B2 600° C. 800° C. test reference 1.5 0.3 1.8 1832.7 32.7 1.00 no cracks no cracks example 1.1 test reference 1.5 0.31.8 19 34.5 32.7 1.06 no cracks no cracks example 1.2 test example 1.11.5 0.3 1.8 20 36.3 32.7 1.11 no cracks no cracks test example 1.2 1.50.3 1.8 37 66.9 32.7 2.05 no cracks no cracks test example 1.3 1.5 0.31.8 54 97.5 32.7 2.98 no cracks no cracks test comparative 1.5 0.3 1.855 99.3 32.7 3.04 cracks cracks example 1.1 found found test comparative1.5 0.3 1.8 56 101.1 32.7 3.09 cracks cracks example 1.2 found found

TABLE 2 wall side length thickness cell outer outer (mm) (mm) pitchcolumn dimension (mm) dimension (mm) thermal shock test C1, C2 D1, D2(mm) number B1 B2 B1/B2 600° C. 800° C. test reference 1.5 0.3 1.8 1832.7 32.7 1.00 no cracks no cracks example 2.1 test reference 1.5 0.31.8 19 34.5 32.7 1.06 no cracks no cracks example 2.2 test example 2.11.5 0.3 1.8 20 36.3 32.7 1.11 no cracks no cracks test example 2.2 1.50.3 1.8 38 68.7 32.7 2.10 no cracks no cracks test example 2.3 1.5 0.31.8 54 97.5 32.7 2.98 no cracks no cracks test comparative 1.5 0.3 1.855 99.3 32.7 3.04 no cracks cracks example 2.1 found test comparative1.5 0.3 1.8 56 101.1 32.7 3.09 cracks cracks example 2.2 found found

TABLE 3 wall side length thickness cell outer side length side lengththermal shock (mm) (mm) pitch column dimension (mm) (mm) (mm) test C1D1, D2 (mm) number B1, B2 C1 C2 C1/C2 600° C. 800° C. test reference 1.50.3 1.8 18 32.7 1.5 1.5 1.00 no no example 3.1 cracks cracks testreference 1.6 0.3 1.9 17 32.6 1.6 1.5 1.07 no no example 3.2 crackscracks test example 3.1 1.7 0.3 2 16 32.3 1.7 1.5 1.13 no no crackscracks test example 3.2 2.25 0.3 2.55 13 33.45 2.25 1.5 1.50 no nocracks cracks test example 3.3 3 0.3 3.3 10 33.3 3 1.5 2.00 no no crackscracks test example 3.4 4.4 0.3 4.7 7 33.2 4.4 1.5 2.93 no no crackscracks test comparative 4.6 0.3 4.9 7 34.6 4.6 1.5 3.07 cracks cracksexample 3.1 found found test comparative 4.8 0.3 5.1 6 30.9 4.8 1.5 3.20cracks cracks example 3.2 found found

TABLE 4 wall side length thickness cell outer side length side lengththermal shock (mm) (mm) pictch column dimension (mm) (mm) (mm) test C1D1, D2 (mm) number B1, B2 C1 C2 C1/C2 600° C. 800° C. test reference 1.50.3 1.8 18 32.7 1.5 1.5 1.00 no no example 4.1 cracks cracks testreference 1.6 0.3 1.9 17 32.6 1.6 1.5 1.07 no no example 4.2 crackscracks test example 4.1 1.7 0.3 2 16 32.3 1.7 1.5 1.13 no no crackscracks test example 4.2 2.25 0.3 2.55 13 33.45 2.25 1.5 1.50 no nocracks cracks test example 4.3 3 0.3 3.3 10 33.3 3 1.5 2.00 no no crackscracks test example 4.4 4.4 0.3 4.7 7 33.2 4.4 1.5 2.93 no no crackscracks test comparative 4.6 0.3 4.9 7 34.6 4.6 1.5 3.07 no cracksexample 4.1 cracks found test comparative 4.8 0.3 5.1 6 30.9 4.8 1.53.20 cracks cracks example 4.2 found found

TABLE 5 wall outer side length thickness cell dimension wall thicknesswall thickness thermal shock (mm) (mm) pitch column (mm) (mm) (mm) testC1, C2 D2 (mm) number B1, B2 D1 D2 D1/D2 600° C. 800° C. test reference1.5 0.4 1.9 18 34.6 0.4 0.4 1.00 no no example 5.1 cracks cracks testreference 1.5 0.37 1.87 18 34.03 0.4 0.37 1.08 no no example 5.2 crackscracks test reference 1.5 0.3 1.8 18 32.7 0.3 0.3 1.00 no no example 5.3cracks cracks test example 5.1 1.5 0.35 1.85 18 33.65 0.4 0.35 1.14 nono cracks cracks test example 5.2 1.5 0.2 1.7 20 34.2 0.4 0.2 2.00 no nocracks cracks test example 5.3 1.5 0.14 1.64 20 32.94 0.4 0.14 2.86 nono cracks cracks test example 5.4 1.5 0.15 1.65 20 33.15 0.3 0.15 2.00no no cracks cracks test comparative 1.5 0.132 1.632 20 32.772 0.4 0.1323.03 cracks cracks example 5.1 found found test comparative 1.5 0.131.63 20 32.73 0.4 0.13 3.08 cracks cracks example 5.2 found found

TABLE 6 side length wall outer wall thickness wall thickness thermalshock (mm) thickness pitch cell dimension (mm) (mm) test C1, C2 D2 (mm)column B1, B2 D1 D2 D1/D2 600° C. 800° C. test reference 1.5 0.4 1.9 1834.6 0.4 0.4 1.00 no no example 6.1 cracks cracks test reference 1.50.37 1.87 18 34.03 0.4 0.37 1.08 no no example 6.2 cracks cracks testreference 1.5 0.3 1.8 18 32.7 0.3 0.3 1.00 no no example 6.3 crackscracks test example 6.1 1.5 0.35 1.85 18 33.65 0.4 0.35 1.14 no nocracks cracks test example 6.2 1.5 0.2 1.7 20 34.2 0.4 0.2 2.00 no nocracks cracks test example 6.3 1.5 0.14 1.64 20 32.94 0.4 0.14 2.86 nono cracks cracks test example 6.4 1.5 0.15 1.65 20 33.15 0.3 0.15 2.00no no cracks cracks test comparative 1.5 0.132 1.632 20 32.772 0.4 0.1323.03 no cracks example 6.1 cracks found test comparative 1.5 0.13 1.6320 32.73 0.4 0.13 3.08 cracks cracks example 6.2 found found

TABLE 7 assembly 9 filter F1 cell 12 cell wall 13 A1 A2 B1 B2 quantityC1 C2 D1 D2 shape type mm mm mm mm number mm mm C1/C2 mm mm D1/D2example 1-1 FIG. test example 1.2 160 80 66 33 9 1.50 1.50 1.00 0.3 0.31.00 6(a) comparative FIG. test reference 80 80 33 33 9 1.50 1.50 1.000.3 0.3 1.00 example 1-1 6(b) example 1.1 comparative FIG. test referece160 80 33 33 15 1.50 1.50 1.00 0.3 0.3 1.00 example 1-2 6(c) example 1.1example 1-2 FIG. test example 2.2 160 80 66 33 9 1.50 1.50 1.00 0.3 0.31.00 6(a) comparative FIG. test example 2.1 80 80 33 33 9 1.50 1.50 1.000.3 0.3 1.00 example 1-3 6(b) comparative FIG. test example 2.1 160 8033 33 15 1.50 1.50 1.00 0.3 0.3 1.00 example 1-4 6(c) sealing materiallayer Temp. 15 peripheral difference temperature E1 E2 portioninsulation ΔT α β γ mm mm E1/E2 mm mm ° C. ° C. ° C. ° C. cracks example1-1 1 1 1 1.5 10 50 450 430 400 none comparative 1 1 1 1.5 10 50 450 430400 none example 1-1 comparative 1 1 1 1.5 10 100 450 430 350 foundexample 1-2 example 1-2 1 1 1 1.5 10 60 450 424 390 none comparative 1 11 1.5 10 60 450 425 390 none example 1-3 comparative 1 1 1 1.5 10 110450 423 340 found example 1-4

TABLE 8 assembly 9 filter F1 cell 12 cell wall 13 A1 A2 B1 B2 quantityC1 C2 D1 D2 shape type mm mm mm mm number mm mm C1/C2 mm mm D1/D2example 2-1 FIG. test example 3.1 160 80 33 33 15 1.70 1.50 1.13 0.3 0.31.00 7(a) example 2-2 FIG. test example 3.2 160 80 33 33 15 2.25 1.501.50 0.3 0.3 1.00 7(a) example 2-3 FIG. test example 3.3 160 80 33 33 153.00 1.50 2.00 0.3 0.3 1.00 7(a) example 2-4 FIG. test example 3.4 16080 33 33 15 4.40 1.50 2.93 0.3 0.3 1.00 7(a) comparative FIG. testreference 160 80 33 33 15 1.50 1.50 1.00 0.3 0.3 1.00 example 2-1 7(b)example 3.1 comparative FIG. test reference 160 80 33 33 15 1.50 1.700.88 0.3 0.3 1.00 example 2-2 7(c) example 3.1 comparative FIG. testreference 160 80 33 33 15 1.50 2.25 0.67 0.3 0.3 1.00 example 2-3 7(c)example 3.2 comparative FIG. test reference 160 80 33 33 15 4.60 1.503.07 0.3 0.3 1.00 example 2-4 7(a) example 3.1 example 2-5 FIG. testexample 4.1 160 80 33 33 15 1.70 1.50 1.13 0.3 0.3 1.00 7(a) example 2-6FIG. test example 4.2 160 80 33 33 15 2.25 1.50 1.50 0.3 0.3 1.00 7(a)example 2-7 FIG. test example 4.3 160 80 33 33 15 3.00 1.50 2.00 0.3 0.31.00 7(a) example 2-8 FIG. test example 4.4 160 80 33 33 15 4.40 1.502.93 0.3 0.3 1.00 7(a) comparative FIG. test reference 160 80 33 33 151.50 1.50 1.00 0.3 0.3 1.00 example 2-5 7(b) example 4.1 comparativeFIG. test reference 160 80 33 33 15 1.50 1.70 0.88 0.3 0.3 1.00 example2-6 7(c) example 4.1 comparative FIG. test reference 160 80 33 33 151.50 2.25 0.67 0.3 0.3 1.00 example 2-7 7(c) example 4.2 comparativeFIG. test reference 160 80 33 33 15 4.60 1.50 3.07 0.3 0.3 1.00 example2-8 7(a) example 4.1 sealing material layer temperature 15 peripheraldifference temperature E1 E2 portion insulation ΔT α β γ mm mm E1/E2 mmmm ° C. ° C. ° C. ° C. cracks example 2-1 1 1 1 1.5 10 93 450 430 357none example 2-2 1 1 1 1.5 10 80 450 430 370 none example 2-3 1 1 1 1.510 76 450 430 374 none example 2-4 1 1 1 1.5 10 70 450 430 380 nonecomparative 1 1 1 1.5 10 100 450 430 350 found example 2-1 comparative 11 1 1.5 10 100 450 434 350 found example 2-2 comparative 1 1 1 1.5 10100 450 440 350 found example 2-3 comparative 1 1 1 1.5 10 65 450 430385 found example 2-4 example 2-5 1 1 1 1.5 10 103 450 423 347 noneexample 2-6 1 1 1 1.5 10 90 450 423 360 none example 2-7 1 1 1 1.5 10 86450 423 364 none example 2-8 1 1 1 1.5 10 80 450 423 370 nonecomparative 1 1 1 1.5 10 110 450 423 340 found example 2-5 comparative 11 1 1.5 10 120 450 434 340 found example 2-6 comparative 1 1 1 1.5 10110 450 440 340 found example 2-7 comparative 1 1 1 1.5 10 75 450 430375 found example 2-8

TABLE 9 assembly 9 filter F1 cell 12 cell wall 13 A1 A2 B1 B2 quantityC1 C2 D1 D2 shape type mm mm mm mm number mm mm C1/C2 mm mm D1/D2example 3-1 FIG. test example 5.1 160 80 33 33 15 1.50 1.50 1.00 0.40.35 1.14 8(a) example 3-2 FIG. test example 5.2 160 80 33 33 15 1.501.50 1.00 0.4 0.2 2.00 8(a) example 3-3 FIG. test example 5.3 160 80 3333 15 1.50 1.50 1.00 0.4 0.14 2.86 8(a) example 3-4 FIG. test example5.4 160 80 33 33 15 1.50 1.50 1.00 0.3 0.15 2.00 8(a) comparative FIG.test reference 160 80 33 33 15 1.50 1.50 1.00 0.3 0.3 1.00 example 3-18(b) example 5.3 comparative FIG. test example 5.1 160 80 33 33 15 1.501.50 1.00 0.35 0.4 0.88 example 3-2 8(c) comparative FIG. test example5.4 160 80 33 33 15 1.50 1.50 1.00 0.15 0.3 0.50 example 3-3 8(c)comparative FIG. test compartive 160 80 33 33 15 1.50 1.50 1.00 0.40.132 3.03 example 3-4 8(a) example 5.1 example 3-5 FIG. test example6.1 160 80 33 33 15 1.50 1.50 1.00 0.4 0.35 1.14 8(a) example 3-6 FIG.test example 6.2 160 80 33 33 15 1.50 1.50 1.00 0.4 0.2 2.00 8(a)example 3-7 FIG. test example 6.3 160 80 33 33 15 1.50 1.50 1.00 0.40.14 2.86 8(a) example 3-8 FIG. test example 6.4 160 80 33 33 15 1.501.50 1.00 0.3 0.15 2.00 8(a) comparative FIG. test reference 160 80 3333 15 1.50 1.50 1.00 0.3 0.3 1.00 example 3-5 8(b) example 6.3comparative FIG. test example 6.1 160 80 33 33 15 1.50 1.50 1.00 0.350.4 0.88 example 3-6 8(c) comparative FIG. test example 6.4 160 80 33 3315 1.50 1.50 1.00 0.15 0.3 0.50 example 3-7 8(c) comparative FIG. testcompartive 160 80 33 33 15 1.50 1.50 1.00 0.4 0.132 3.03 example 3-88(a) example 6.1 sealing material layer Temp. 15 peripheral differencetemperature E1 E2 portion insulation ΔT α β γ mm mm E1/E2 mm mm ° C. °C. ° C. ° C. cracks example 3-1 1 1 1 1.5 10 91 450 423 359 none example3-2 1 1 1 1.5 10 79 450 428 371 none example 3-3 1 1 1 1.5 10 73 450 424377 none example 3-4 1 1 1 1.5 10 85 450 425 365 none comparative 1 1 11.5 10 100 450 430 350 found example 3-1 comparative 1 1 1 1.5 10 95 450435 355 found example 3-2 comparative 1 1 1 1.5 10 110 450 430 340 foundexample 3-3 comparative 1 1 1 1.5 10 68 450 430 382 found example 3-4example 3-5 1 1 1 1.5 10 101 450 416 349 none example 3-6 1 1 1 1.5 1090 450 420 360 none example 3-7 1 1 1 1.5 10 82 450 415 368 none example3-8 1 1 1 1.5 10 95 450 413 355 none comparative 1 1 1 1.5 10 110 450423 340 found example 3-5 comparative 1 1 1 1.5 10 105 450 428 345 foundexample 3-6 comparative 1 1 1 1.5 10 120 450 423 330 found example 3-7comparative 1 1 1 1.5 10 75 450 430 375 found example 3-8

TABLE 10 assembly 9 filter F1 cell 12 cell wall 13 A1 A2 B1 B2 quantityC1 C2 D1 D2 Shape type mm mm mm mm number mm mm C1/C2 mm mm D1/D2example 4-1 FIG. test reference 160 80 33 33 15 1.50 1.50 1.00 0.3 0.31.00 9(a) example 1.1 example 4-2 FIG. test reference 160 80 33 33 151.50 1.50 1.00 0.3 0.3 1.00 9(a) example 1.1 example 4-3 FIG. testreference 160 80 33 33 15 1.50 1.50 1.00 0.3 0.3 1.00 9(a) example 1.1example 4-4 FIG. test reference 160 80 33 33 15 1.50 1.50 1.00 0.3 0.31.00 9(a) example 1.1 example 4-5 FIG. test reference 160 80 33 33 151.50 1.50 1.00 0.3 0.3 1.00 9(a) example 1.1 comparative FIG. testreference 160 80 33 33 15 1.50 1.50 1.00 0.3 0.3 1.00 example 4-1 9(b)example 1.1 comparative FIG. test reference 160 80 33 33 15 1.50 1.501.00 0.3 0.3 1.00 example 4-2 9(c) example 1.1 comparative FIG. testreference 160 80 33 33 15 1.50 1.50 1.00 0.3 0.3 1.00 example 4-3 9(a)example 1.1 example 4-6 FIG. test reference 160 80 33 33 15 1.50 1.501.00 0.3 0.3 1.00 9(a) example 2.1 example 4-7 FIG. test reference 16080 33 33 15 1.50 1.50 1.00 0.3 0.3 1.00 9(a) example 2.1 example 4-8FIG. test reference 160 80 33 33 15 1.50 1.50 1.00 0.3 0.3 1.00 9(a)example 2.1 example 4-9 FIG. test reference 160 80 33 33 15 1.50 1.501.00 0.3 0.3 1.00 9(a) example 2.1 example 4-10 FIG. test reference 16080 33 33 15 1.50 1.50 1.00 0.3 0.3 1.00 9(a) example 2.1 comparativeFIG. test reference 160 80 33 33 15 1.50 1.50 1.00 0.3 0.3 1.00 example4-4 9(b) example 2.1 comparative FIG. test reference 160 80 33 33 151.50 1.50 1.00 0.3 0.3 1.00 example 4-5 9(c) example 2.1 comparativeFIG. test reference 160 80 33 33 15 1.50 1.50 1.00 0.3 0.3 1.00 example4-6 9(a) example 2.1 sealing material layer 15 peripheral Temp. E1 E2portion insulation difference temperature mm mm E1/E2 mm mm β − γ α β γcracks example 4-1 1.05 1 1.05 1.5 10 75 450 425 350 none example 4-2 21 2 1.5 10 75 450 425 350 none example 4-3 3 1 3 1.5 10 65 450 415 350none example 4-4 4 1 4 1.5 10 20 450 370 350 none example 4-5 5 1 5 1.510 0 450 350 350 none comparative 1 1 1 1.5 10 80 450 430 350 foundexample 4-1 comparative 1 2 0.5 1.5 10 130 450 440 310 found example 4-2comparative 6 1 6 1.5 10 −20 450 330 350 found example 4-3 example 4-61.05 1 1.05 1.5 10 75 450 415 340 none example 4-7 2 1 2 1.5 10 75 450415 340 none example 4-8 3 1 3 1.5 10 71 450 411 340 none example 4-9 41 4 1.5 10 25 450 365 340 none example 4-10 5 1 5 1.5 10 2 450 342 340none comparative 1 1 1 1.5 10 83 450 423 340 found example 4-4comparative 1 2 0.5 1.5 10 132 450 432 300 found example 4-5 comparative6 1 6 1.5 10 −10 450 330 340 found example 4-6

TABLE 11 sealing material assembly 9 filter F1 SiC layer 15 long shortlong short average long short axis axis side side diameter silica axisaxis A1 A2 B1 B2 quantity ceramic 0.3 μm sol CMC water E1 E2 shape typemm mm mm mm number fibers wt % wt % wt % wt % wt % mm mm E1/E2 example5-1 FIG. 10(a) test reference 160 80 33 33 15 31.10 15.00 14.40 0.5039.00 1 1 1 example 1.1 example 5-2 FIG. test reference 160 80 33 33 1534.00 7.50 19.00 0.50 39.00 1 1 1 10(a) example 1.1 example 5-3 FIG.test reference 160 80 33 33 15 30.30 3.00 27.20 0.50 39.00 1 1 1 10(a)example 1.1 example 5-4 FIG. test reference 160 80 33 33 15 31.30 0.5028.70 0.50 39.00 1 1 1 10(a) example 1.1 comparative FIG. test reference160 80 33 33 15 23.30 30.20 7.00 0.50 39.00 1 1 1 example 5-1 10(b)example 1.1 comparative FIG. test reference 160 80 33 33 15 13.50 40.007.00 0.50 39.00 1 1 1 example 5-2 10(c) example 1.1 comparative FIG.test reference 160 80 33 33 15 31.30 0.20 29.00 0.50 39.00 1 1 1 example5-3 10(a) example 1.1 example 5-5 FIG. test reference 160 80 33 33 1531.10 15.00 14.40 0.50 39.00 1 1 1 10(a) example 2.1 example 5-6 FIG.test reference 160 80 33 33 15 34.00 7.50 19.00 0.50 39.00 1 1 1 10(a)example 2.1 example 5-7 FIG. test reference 160 80 33 33 15 30.30 3.0027.20 0.50 39.00 1 1 1 10(a) example 2.1 example 5-8 FIG. test reference160 80 33 33 15 31.30 0.50 28.70 0.50 39.00 1 1 1 10(a) example 2.2comparative FIG. test reference 160 80 33 33 15 23.30 30.20 7.00 0.5039.00 1 1 1 example 5-4 10(b) example 2.3 comparative FIG. testreference 160 80 33 33 15 13.50 40.00 7.00 0.50 39.00 1 1 1 example 5-510(c) example 2.4 comparative FIG. test reference 160 80 33 33 15 31.300.20 29.00 0.50 39.00 1 1 1 example 5-6 10(a) example 2.1 thermalconductivity long short axis axis peripheral Temp. G1 G2 portioninsulation difference temperature W/m · K W/m · K G1/G2 mm mm β − γ α βγ cracks example 5-1 0.2 0.3 0.67 1.5 10 76 450 426 350 none example 5-20.15 0.3 0.50 1.5 10 75 450 425 350 none example 5-3 0.1 0.3 0.33 1.5 1065 450 415 350 none example 5-4 0.06 0.3 0.20 1.5 10 0 450 350 350 nonecomparative 0.3 0.3 1.00 1.5 10 80 450 430 350 found example 5-1comparative 0.6 0.3 2.00 1.5 10 90 450 440 350 found example 5-2comparative 0.05 0.3 0.17 1.5 10 −20 450 330 350 found example 5-3example 5-5 0.2 0.3 0.67 1.5 10 76 450 416 340 none example 5-6 0.15 0.30.50 1.5 10 75 450 415 340 none example 5-7 0.1 0.3 0.33 1.5 10 71 450411 340 none example 5-8 0.06 0.3 0.20 1.5 10 2 450 342 340 nonecomparative 0.3 0.3 1.00 1.5 10 83 450 423 340 found example 5-4comparative 0.6 0.3 2.00 1.5 10 92 450 432 340 found example 5-5comparative 0.05 0.3 0.17 1.5 10 −10 450 330 340 found example 5-6

TABLE 12 assembly 9 filter F1 SiC long short long short average axisaxis axis axis ceramic diameter silica A1 A2 B1 B2 quantity fibers 0.3μsol CMC water shape type mm mm mm mm number wt % wt % wt % wt % wt %total example 6-1 FIG. test reference 160 80 33 33 15 23.30 30.20 7.000.50 39.00 100.00 10(a) example 1.1 example 6-2 FIG. test reference 16080 33 33 15 23.30 30.20 7.00 0.50 39.00 100.00 10(a) example 1.1 example6-3 FIG. test reference 160 80 33 33 15 23.30 30.20 7.00 0.50 39.00100.00 10(a) example 1.1 example 6-4 FIG. test reference 160 80 33 33 1523.30 30.20 7.00 0.50 39.00 100.00 10(a) example 1.1 comparative FIG.test reference 160 80 33 33 15 23.30 30.20 7.00 0.50 39.00 100.00example 6-1 10(b) example 1.1 comparative FIG. test reference 160 80 3333 15 23.30 30.20 7.00 0.50 39.00 100.00 example 6-2 10(c) example 1.1comparative FIG. test reference 160 80 33 33 15 23.30 30.20 7.00 0.5039.00 100.00 example 6-3 10(a) example 1.1 example 6-5 FIG. testreference 160 80 33 33 15 23.30 30.20 7.00 0.50 39.00 100.00 10(a)example 2.1 example 6-6 FIG. test reference 160 80 33 33 15 23.30 30.207.00 0.50 39.00 100.00 10(a) example 2.1 example 6-7 FIG. test reference160 80 33 33 15 23.30 30.20 7.00 0.50 39.00 100.00 10(a) example 2.1example 6-8 FIG. test reference 160 80 33 33 15 23.30 30.20 7.00 0.5039.00 100.00 10(a) example 2.1 comparative FIG. test reference 160 80 3333 15 23.30 30.20 7.00 0.50 39.00 100.00 example 6-4 10(b) example 2.1comparative FIG. test reference 160 80 33 33 15 23.30 30.20 7.00 0.5039.00 100.00 example 6-5 10(c) example 2.1 comparative FIG. testreference 160 80 33 33 15 23.30 30.20 7.00 0.50 39.00 100.00 example 6-610(a) example 2.1 sealing material layer 15 outer sealing material longshort short long axis axis axis axis Temp. E1 E2 H2 H1 insulationdifference temperature mm mm E1/E2 mm mm H2/H1 mm β − γ α β γ cracksexample 6-1 1 1 1 1.5 1.6 0.94 10 73 450 423 350 none example 6-2 1 1 11.5 10.0 0.15 10 70 450 420 350 none example 6-3 1 1 1 1.5 20.0 0.08 1060 450 410 350 none example 6-4 1 1 1 1.5 25.0 0.06 10 0 450 350 350none comparative 1 1 1 1.5 1.5 1.00 10 80 450 430 350 found example 6-1comparative 1 1 1 1.5 1.0 1.50 10 90 450 440 350 found example 6-2comparative 1 1 1 1.5 30.0 0.05 10 −30 450 320 350 found example 6-3example 6-5 1 1 1 1.5 1.6 0.94 10 80 450 420 340 none example 6-6 1 1 11.5 10.0 0.15 10 78 450 418 340 none example 6-7 1 1 1 1.5 20.0 0.08 1068 450 408 340 none example 6-8 1 1 1 1.5 25.0 0.06 10 2 450 342 340none comparative 1 1 1 1.5 1.5 1.00 10 83 450 423 340 found example 6-4comparative 1 1 1 1.5 1.0 1.50 10 98 450 438 340 found example 6-5comparative 1 1 1 1.5 30.0 0.05 10 −10 450 330 340 found example 6-6

TABLE 13 sealing material assembly 9 filter F1 layer 15 outer sealingmaterial long short long short long short long short axis axis axis axisaxis axis axis axis A1 A2 B1 B2 quantity E1 E2 H1 H2 shape type mm mm mmmm number mm mm E1/E2 mm mm H1/H2 example 7-1 FIG. test reference 160 8033 33 15 1 1 1 1.5 1.5 1.00 10(a) example 1.1 example 7-2 FIG. testreference 160 80 33 33 15 1 1 1 1.5 1.5 1.00 10(a) example 1.1 example7-3 FIG. test reference 160 80 33 33 15 1 1 1 1.5 1.5 1.00 10(a) example1.1 comparative FIG. test reference 160 80 33 33 15 1 1 1 1.5 1.5 1.00example 7-1 10(b) example 1.1 comparative FIG. test reference 160 80 3333 15 1 1 1 1.5 1.5 1.00 example 7-2 10(c) example 1.1 comparative FIG.test reference 160 80 33 33 15 1 1 1 1.5 1.5 1.00 example 7-3 10(a)example 1.1 example 7-4 FIG. test reference 160 80 33 33 15 1 1 1 1.51.5 1.0 10(a) example 2.1 example 7-5 FIG. test reference 160 80 33 3315 1 1 1 1.5 1.5 1 10(a) example 2.1 example 7-6 FIG. test reference 16080 33 33 15 1 1 1 1.5 1.5 1 10(a) example 2.1 comparative FIG. testreference 160 80 33 33 15 1 1 1 1.5 1.5 1 example 7-4 10(b) example 2.1comparative FIG. test reference 160 80 33 33 15 1 1 1 1.5 1.5 1 example7-5 10(c) example 2.1 comparative FIG. test reference 160 80 33 33 15 11 1 1.5 1.5 1 example 7-6 10(a) example 2.1 outer insulation materialshort long axis axis Temp. I2 I1 difference temperature mm mm I2/I1 β −γ α β γ cracks example 7-1 10 11 0.91 73 450 423 350 none example 7-2 1020 0.50 70 450 420 350 none example 7-3 10 30 0.33 0 450 350 350 nonecomparative 10 10 1.00 80 450 430 350 found example 7-1 comparative 1035 0.29 90 450 440 350 found example 7-2 comparative 10 9 1.11 −30 450320 350 found example 7-3 example 7-4 10 11 0.91 80 450 420 340 noneexample 7-5 10 20 0.50 78 450 418 340 none example 7-6 10 30 0.33 2 450342 340 none comparative 10 10 1.00 83 450 423 340 found example 7-4comparative 10 35 0.29 98 450 438 340 found example 7-5 comparative 10 91.11 −10 450 330 340 found example 7-6

1. A ceramic filter assembly comprising: major and minor axes; aplurality of columnar honeycomb filters adhered together; the pluralityof columnar honeycomb filters being made of a porous ceramic sinteredmaterial with a ceramic sealing material layer and having end faces anda generally elliptical cross sectional shape when cut parallel to theend faces of the plurality of honeycomb filters; the plurality ofhoneycomb filters including a honeycomb filter having a rectangularcross sectional shape when cut parallel to the end faces and providedwith a long side having a length B1 and a short side having a length B2in which the ratio B1/B2 is between 1.1 and 3.0; the honeycomb filterbeing arranged so that the long side and the short side of the honeycombfilter are respectively parallel to the major axis and the minor axis ofthe assembly.
 2. A ceramic filter assembly comprising; major and minoraxes; a plurality of columnar honeycomb filters adhered together; theplurality of columnar honeycomb filters being made of a porous ceramicsintered material with a ceramic sealing material layer and having endfaces and a generally elliptical cross sectional shape when cut parallelto end faces of the plurality of honeycomb filters; each honeycombfilter including a plurality of rectangular cells extending along anaxis of the filter with each cell provided with a long side having alength C1 and a short side having a length C2 in which the ratio C1/C2is between 1.1 and 3.0; and the plurality of honeycomb filters beingarranged so that the long sides of the cells are parallel to the majoraxis of the assembly and the short sides of the cells are parallel tothe minor axis of the assembly.
 3. A ceramic filter assembly comprising:major and minor axes; a plurality of columnar honeycomb filters adheredtogether; the plurality of columnar honeycomb filters being made of aporous ceramic sintered material with a ceramic sealing material layerand having end faces and a generally elliptical cross sectional shapewhen cut parallel to the end faces of the plurality of honeycombfilters; each honeycomb filter including an axis and a plurality ofrectangular cells extending along the axis of the filter and defined byrelatively thick cell walls and relatively thin walls that areorthogonal to each other; and the plurality of honeycomb filters beingarranged so that the relatively thick cell walls are parallel to themajor axis of the assembly and the relatively thin cell walls areparallel to the minor axis of the assembly.
 4. The ceramic filterassembly as claimed in claim 3, wherein when the thickness of therelatively thick cell walls is represented by D1 and the thickness ofthe relatively thin cell walls is represented by D2, D1 and D2 arewithin a range of 0.1 to 0.5 mm, and the ratio D1/D2 is 3 or less.
 5. Aceramic filter assembly comprising: a major axis; a plurality ofcolumnar honeycomb filters including outer surfaces adhered together;the plurality of colunmar honeycomb filters being made of a porousceramic sintered material with a ceramic sealing material layer andhaving end faces and a generally elliptical cross sectional shape whencut parallel to the end faces of the plurality of honeycomb filters; andthe ceramic sealing material layer including, a first sealing materiallayer extending parallel to the major axis of the assembly, and a secondsealing material layer extending orthogonal to the major axis of theassembly, wherein the first sealing material layer is thicker than thesecond sealing material layer.
 6. The ceramic filter assembly as claimedin claim 5, wherein when the thickness of the first sealing materiallayer is represented by E1 and the thickness of the second sealingmaterial layer is represented by E2, E1 and E2 are between 0.3 mm to 3mm, and the ratio E1/E2 is 1.05 or greater and 5 or less.
 7. A ceramicfilter assembly comprising: a major axis; a plurality of columnarhoneycomb filters adhered together; the plurality of columnar honeycombfilters being made of a porous ceramic sintered material with a ceramicsealing material layer and having end faces and a generally ellipticalcross sectional shape when cut parallel to the end faces of theplurality of honeycomb filters; and the ceramic sealing material layerincluding, a first sealing material layer parallel to the major axis ofthe assembly, and a second sealing material layer orthogonal to themajor axis of the assembly, the first sealing material layer havingthermal conductivity that is lower than the thermal conductivity of thesecond sealing material layer.
 8. The ceramic filter assembly as claimedin claim 7, wherein when the thermal conductivity of the first sealingmaterial layer is represented by G1 and the thermal conductivity of thesecond sealing material layer is represented by G2, the ratio G1/G2 is0.2 or greater and 0.7 or less.
 9. A ceramic filter assembly comprising:an outer periphery, major, and minor axes; a plurality of columnarhoneycomb filters adhered together; the plurality of columnar honeycombfilters being made of a porous ceramic sintered material with a ceramicsealing material layer made of ceramic and having end faces and agenerally elliptical cross sectional shape when cut parallel to the endfaces of the plurality of honeycomb filters; an outer sealing materiallayer made of ceramic and formed on the periphery of the assembly; andthe outer sealing material layer including a first portion located alongan extension of the major axis of the assembly that is thicker than asecond portion located along an extension of the minor axis of theassembly.
 10. The ceramic filter assembly as claimed in claim 9, whereinwhen the thickness of the first portion is represented by H1 and thethickness of the second portion is represented by H2, the ratio H2/H1 is0.06 or greater and 0.95 or less.
 11. The ceramic filter assembly asclaimed in claim 9, wherein the outer sealing material layer is formedfrom two or more types of a coating material having different thermalconductivity.
 12. A canning body comprising: a ceramic filter assemblyincluding major and minor axes and a plurality of columnar honeycombfilters adhered together, the plurality of columnar honeycomb filtersbeing made of a porous ceramic sintered material with an inner sealingmaterial layer made of ceramic and having end faces and a generallyelliptical cross sectional shape when cut parallel to the end faces ofthe plurality of honeycomb filters; a tubular casing for accommodatingthe ceramic filter assembly; and a thermal insulation material arrangedbetween the casing and the ceramic filter assembly, the thermalinsulation material including a first portion located along an extensionof the major axis of the assembly and a second portion located along anextension of the minor axis of the assembly, wherein the first portionis thicker than the second portion.
 13. The canning body as claimed inclaim 12, wherein when the thickness of the first portion is representedby I1 and the thickness of the second part is represented by 12, theratio I2/I1 is 0.30 or greater and 0.91 or less.
 14. The canning body asclaimed in claim 12, wherein the thermal insulation material is made oftwo or more types of material having different thermal conductivity. 15.A columnar honeycomb filter comprising: a plurality of rectangular cellsextending along an axial direction of the honeycomb filter; eachrectangular cell being defined by a relatively thick cell wall and arelatively thin cell wall that are orthogonal to each other, and beingmade of a porous ceramic sintered material; and the relatively thickcell walls having a uniform wall thickness and the relatively thin cellwalls having a uniform wall thickness.
 16. The columnar honeycomb filteras claimed in claim 15, wherein when the thickness of the relativelythick cell wall is represented by D1 and the thickness of the relativelythin cell wall is represented by D2, the ratio D1/D2 is 3 or less. 17.The ceramic filter assembly as claimed in claim 1, wherein the porousceramic sintered material includes silicon carbide and metal silicon.18. The ceramic filter assembly as claimed in claim 1, furthercomprising a catalyst.
 19. A ceramic filter assembly comprising: aplurality of columnar honeycomb filters adhered together; the pluralityof honeycomb filters being made of a porous ceramic sintered materialwith a ceramic sealing material layer and having end faces and agenerally elliptical cross sectional shape when cut parallel to the endfaces of the plurality of honeycomb filters, wherein when a hypotheticalfirst straight line intersects the generally elliptical contour at twopoints in which the distance therebetween is maximum and a hypotheticalsecond straight line orthogonal to the first straight line intersectsthe generally elliptical contour at two points in which the distancetherebetween is maximum, the number of sealing material layers the firststraight line of the assembly traverses is less than or equal to thenumber of sealing material layers the second straight line traverses.20. The ceramic filter assembly as claimed in claim 2, wherein theporous ceramic sintered material includes silicon carbide and metalsilicon.
 21. The ceramic filter assembly as claimed in claim 2, furthercomprising a catalyst.
 22. The honeycomb filter as claimed in claim 15,wherein the porous ceramic sintered material includes silicon carbideand metal silicon.
 23. The columnar honeycomb filter as claimed in claim15, further comprising a catalyst.